How a Key Enzyme Repairs Sun-Damaged DNA

BraveHeart writes "Researchers have long known that mammals, including humans, lack a key enzyme — one possessed by most of the animal kingdom and even plants — that reverses severe sun damage. For the first time, researchers have witnessed how this enzyme works at the atomic level to repair sun-damaged DNA. 'Normal sunscreen lotions convert UV light to heat, or reflect it away from our skin. A sunscreen containing photolyase could potentially heal some of the damage from UV rays that get through.'"

Comments

However,

[wasmoke]

The ever present question remains: how long until we can see a viable product on the market?

Re:However,

[interkin3tic]

The ever present question remains: how long until we can see a viable product on the market?

Maybe never. Science is at least partially driven by curiosity, not just "what useful things can we get out of it."

Other DNA damage?

[kombipom]

Any reason why this couldn't be used to repair damage from other forms of radiation or carcinogens?

Re:Other DNA damage?

[MachDelta]

IANAB but as far as I understand it photolyase only repairs a certain type of damage found between adjacent cytosine and thymine (or uracil) units. That just happens to be the type of damage most commonly caused by UV radiation, so the enzyme can be understood as a fix for that particular method of damage. Other forms of radiation or chemical carcinogens effect DNA in a variety of other ways, most of which photolyase won't have an affinity for, rendering it ineffective.

As a car analogy... photolyase is like caranuba wax. It'll fix the small scratches and minor dings, but if some jackass comes along and smashes your windows and kicks in your doors you won't have much luck trying to buff it out. :)

Re:Other DNA damage?

[MachDelta]

Er, I meant affect.

Damnit. Now I have to go sit in the corner. :(

Re:Other DNA damage?

[Thanshin]

IANAB but as far as I understand it photolyase only repairs a certain type of damage found between adjacent cytosine and thymine (or uracil) units.

I wonder what has that to do with bowyery.

Re:Other DNA damage?

[fabioalcor]

This is the first time I see a self grammar Nazi.

Re:Other DNA damage?

[infinitelink]

In this milieu, "the body" refers to human beings, while the article (and the summary) points out that human beings do not have this enzyme.

Re:Other DNA damage?

[Shakrai]

This is the first time I saw a self grammar Nazi.

FTFY ;)

Re:Other DNA damage?

[Ungrounded Lightning]

This is the first time I see a self grammar Nazi.

You obviously haven't been paying attention to my posts. B=)

Re:Other DNA damage?

[lpq]

I like that analogy!
++ for amusing and pertinent!

Re:Other DNA damage?

[bradbury]

There are ~150 proteins in the human genome that operate through ~5 processes (some overlap) to maintain and repair DNA damage. DNA damage from many carcinogens would modify individual bases which are maintained through Base Excision repair or Mismatch Repair [2]. Radiation on the other hand (at least the ionizing kind -- X-rays and Gamma-rays) produces free radicals in the cells and can induce single strand and double strand breaks in the DNA backbone. DNA double strand breaks are potentially the most harmful as they must be repaired and in non-dividing cells the probable repair process is the Non-Homologous-End-Joining (NHEJ) which involves the WRN and DCLRE1C proteins which have exonuclease activities which can delete DNA bases from the DNA strands. These in turn introduce microdeletions (or in some cases microinsertions) which can corrupt gene sequences producing downstream problems (unfolded proteins, malfunctioning proteins, diminished protein production, cell death, etc.).

The photolyase enzyme which is involved in repairing thymine dimers (produced by UV radiation) is much simpler than most of the other DNA repair mechanisms. All known organisms with the possible exception of Deinococcus radiodurans and its close relatives repair DNA double strand breaks using similar, potentially genome corrupting, processes because not repairing such breaks is much worse than repairing them and potentially corrupting a small portion of the genome. The problem is that the accumulation of such botched repair processes likely plays a major role in aging. (Think of your body as an running instance of Microsoft Word and cosmic rays are going through your RAM flipping bits in memory. One hour the print function stops working, next hour the copy function stops working, next hour the dictionary lookup stops working, etc. [1] eventually it gets to the point where nothing works and you have to reload it. Bodies are currently not reloadable).

1. We are assuming here that the bit-flipping isn't introducing segmentation violations, etc. Bodies tend to be fairly error tolerant due to the cellular redundancy but the faulty fixups do accumulate over time.
2. All of the DNA repair process have greater or lesser degrees of reliability. Base excision repair is likely to work most of the time. Mismatch repair can be much more a roll of the dice.

It is not that straightforward

[Anonymous Coward]

Well, if it was present with all plants and animals (except mammals) why did evolution lose such a "useful" enzyme? Or more importantly, what functionality did the body get while losing it? Without understanding these basic questions, it would be foolhardy to get such a product and start using it all over our body.

Re:It is not that straightforward

[BlackGriffen]

Things can disappear due to genetic drift. If the tail of mammals living underground or nocturnal for a long time is true, for instance, then losing the gene to repair sun damage wouldn't be a big deal. Considering that color vision is rare in mammals, another thing only useful in broad daylight, it wouldn't surprise me if it was just lost randomly. I mean, do you really think it's useless to have 3 color vision? Or 4, as is common in many other animal kingdoms? Add in the fact that so many mammals are covered in enough fur/hair that they don't have that much sun exposure and a loss by genetic drift is a virtual shoe-in.

Same thing with human's inability to produce our own vitamin C.

Re:It is not that straightforward

[Thanshin]

Well, if it was present with all plants and animals (except mammals) why did evolution lose such a "useful" enzyme?

I've always imagined the evolutionary criteria as "The absolute minimum required to maximize chances of reproduction" and not "Everything that might be useful".

Otherwise we'd have poisonous fangs, wings, the ability to digest cellulose and, possibly, firebreath not dependant on a mexican diet.

Re:It is not that straightforward

[GospelHead821]

Cancer is a disease that affects organisms late in life. Generally speaking, they will have already had an opportunity to reproduce by the time that they develop cancer. The introduction of this mutation could have been completely coincidental and it would not have affected the reproductive fitness of the organisms that had it. You might suggest that damage to DNA has consequences besides cancer but it actually doesn't, really. If a cell's DNA becomes too corrupt but the cell doesn't become cancerous as a result, just that one cell is likely to die. You're constantly making new skin cells anyway.

Re:It is not that straightforward

[NoKaOi]

Aren't most mammals generally, well, furry? Perhaps being covered in fur reduces UV exposure to the skin so such an enzyme is no longer needed, therefore furry critters with more photolyase don't tend to reproduce more?

Re:It is not that straightforward

[Genda]

Things come and go for reasons other than natural selection... which is why such theories as punctuated equilibrium have such importance. Most human beings have an amazingly similar genetic makeup. We also have an unusually high number of genetic diseases. Both of these facts are due to the very high probability that our species almost went extinct about 27,000 years ago, and that there may have been fewer than 1,000 individuals left on the planet. This would have resulted in a tremendous loss of genetic diversity, and many interesting human traits may well have disappeared... and the only determining factor was those who were furthest from the cataclysm and had enough resources to survive the aftermath... in short... LUCK.

Re:It is not that straightforward

[jamesh]

I've always imagined the evolutionary criteria as "The absolute minimum required to maximize chances of reproduction" and not "Everything that might be useful".

I think it's more like "The absolute minimum required to be better at reproducing than everyone else".

Otherwise we'd have poisonous fangs, wings, the ability to digest cellulose and, possibly, firebreath not dependant on a mexican diet.

I've met a few people with a few of those attributes and it turned out to be not quite as useful as ensuring reproduction as you might think. Firebreath tends to be a bit of a turnoff.

Re:It is not that straightforward

[petterb]

I figure we don't have it, because basically we haven't had the need for it. 100'000 years ago when we were running around in Africa, we were exposed to the sun - all the time. That means we had a pretty good base to withstand the rays of the sun. Besides, we probably covered ourselves in mud (like the elephants), or stayed in the shades during the most intensive hours of the day.

Nowadays, most of us are sitting inside when the sun is up, and we don't gradually build up this tolerance. And then when we have 2 weeks off, we're suddenly laying flat out on some beach somewhere, totally exposed to the sun the entire day. No wonder our skin gets damaged.

Rather then waiting for something to fix skin damage, learn how to avoid damaging your skin in the first place instead.

Re:It is not that straightforward

[Anonymous Coward]

Firebreath tends to be a bit of a turnoff.

I, for one, ...

*puts on shades* ...think it's hot.

Re:It is not that straightforward

[A beautiful mind]

Cancer is a disease that affects organisms late in life. Generally speaking, they will have already had an opportunity to reproduce by the time that they develop cancer. The introduction of this mutation could have been completely coincidental and it would not have affected the reproductive fitness of the organisms that had it.

I was about to post something similar to what you wrote, but you were quicker. I'd just like to add the minor point that while cancer isn't that bad for the reproductive success of a mammal, it's effect is not zero or entirely negligible. Since we're really talking about the self-replication of genetic data, which is what actually let's us explain close-kin relations on a biological level, cancer's effect and protection against cancer does have effects on the successfulness of one bundle of genetic data against another one.

Someone developing cancer at an older age loses the possibility of reproduction. A human male is more than capable of fathering an offspring over the age of 45. Dieing of cancer can also have a bad impact on the success of your offspring, because they lose the father's/mother's support. It's not only about an organisms' direct reproductive success, but also about the success of the genetic data that lives on in genetically closely related members of a species.

Re:It is not that straightforward

[nedlohs]

That isn't how evolution works. Why would such an enzyme be "useful" in terms of survival and reproduction to fur covered animals that spend the daytime hidden in burrows, for example?

Re:It is not that straightforward

[nedlohs]

It's mammals not humans - which means it predates humans and hence human habitats and so on are completely irrelevant since there were no humans in existence when this was lost*.

* assuming, without RTFA, the orders of magnitude more likely case that mammals (or some pre-mammal) lost it, rather than everything else evolved it independently.

Re:It is not that straightforward

[Guignol]

No, parent was not meaning 'here is a winner genetic drift ' (that would be shoo-in) he meant, this is a genetic drift you can't easily get rid of because it has a shoe in, preventing you from closing the door ;)
Also, I'm just kidding

Re:It is not that straightforward

[shentino]

Considering how many people have died from scurvy I'm not sure that inability to produce vitamin C was an evolutionarily sound decision.

Re:It is not that straightforward

[Bryan3000000]

Fur covered body makes more sense as a replacement to cover such drift. Fur is pretty effective at blocking the sun. Also melanin. Mammals without fur and/or light colored skin get the shaft. Of sunlight.

Re:It is not that straightforward

[flink]

Yeaaaaaaaaaaahhhhhhhhhh!

Re:It is not that straightforward

[moonbender]

Quit anthropomorphising evolution. It hates that!

Re:It is not that straightforward

[blackraven14250]

Scurvy wasn't nearly as big an issue before long sea voyages started.

Re:It is not that straightforward

[blackraven14250]

Someone developing cancer at an older age loses the possibility of reproduction. A human male is more than capable of fathering an offspring over the age of 45. Dieing of cancer can also have a bad impact on the success of your offspring, because they lose the father's/mother's support. It's not only about an organisms' direct reproductive success, but also about the success of the genetic data that lives on in genetically closely related members of a species.

That's all well and good, but consider that we're talking about the entire expanse of mammalian evolution, not the very short (and recent) period of time where being over 45 years old means you have more money and are likely to be more stable in life. Over the course of mammalian evolution, being over 45 meant you were an outlier.

Re:It is not that straightforward

[SleazyRidr]

See, back in the olden days, mammals all had detachable tails that would go off and live underground while the rest of you went about your day-to-day business. It lead to really weird tan-lines, and most of you would get burned to a crisp, but your tail would still be lilly-white.

Re:It is not that straightforward

[SleazyRidr]

I think it's more like "The absolute minimum required to be better at reproducing than everyone else".

No it isn't. If you can survive long enough to produce offspring, you win evolution.

Re:It is not that straightforward

[Ungrounded Lightning]

Also melanin. Mammals without fur and/or light colored skin get the shaft. Of sunlight.

Melanin helps a lot but it's far from a perfect shield. (For starters, some light has to make it through to avoid rickets through lack of sunlight-catalyzed vitamin D synthesis if the diet isn't rich in D {and similar problems with vitamin A deficiency} - which is why those branches of humanity that lived more poleward for a few hundred generations switched to only light-triggered melanin production or just lost the ability to tan {except in spots} at all.)

Dark-skinned people still get sun-damage-genetic-noise skin diseases. They just don't get them as often.

Re:It is not that straightforward

[mrchaotica]

Over the course of [human*] evolution, being over 45 meant you were an outlier.

No it didn't; living past 45 has always been pretty common among people who managed to survive childhood. The high child mortality rate in the past used to skew the average.

(* It doesn't make sense to talk about average lifespans over the whole of mammalian evolution, since different species have widely varying lifespans that depend mostly on factors other than the age of the species.)

Re:It is not that straightforward

[ceoyoyo]

You might, but your genes only win if they get to be in MORE offspring than most of the others and those offspring are also better at putting genes in more offspring.

Re:It is not that straightforward

[ceoyoyo]

There's quite good evidence that grandparents contribute very positively to their grandchildren's well-being long after their actively reproductive age. Grandma is quite capable of sitting around pounding palm fibre into edible carbohydrates, after all (in fact, she's usually better at it than the whippersnappers), she tends to share most with her close kin, and she's not busy trying to get pregnant, risking childbirth, or making risky investments of energy in nursing, pregnancy or child rearing. A quite good theory for the existence of menopause in women is that it ends their childbearing years when the risk of childbirth and rearing becomes too high but leaves them alive to help support their close relatives.

Re:It is not that straightforward

[bradbury]

> You might suggest that damage to DNA has consequences besides cancer but it actually doesn't, really.

You need to go do some more research. Somatic mutation is probably the primary cause of "aging". There are ~150 DNA repair proteins operating through 4-5 repair mechanisms. One in particular, Non-Homologous-End-Joining (NHEJ) which is the primary repair mechanism for DNA double strand breaks in mammals, particularly in non-replicating cells, involves two proteins the WRN protein and the DCLRE1C (Artemis) protein which have exonuclease activity. That activity will chew up your DNA in the process of repair and introduce microdeletions or microinsertions in the genome in the process of repairing said double strand breaks. Those in turn will introduce frame shift mutations or premature stop mutations or splice site mutations which in turn will increase the probability that you will have proteins in those cells which will never fold properly. Unfolded proteins activate endoplasmic reticulum or mitochondrial unfolded protein responses which contribute to the cell functioning less efficiently and/or committing suicide. Michael Leiber, a Prof. at UCLA has estimated by the time you hit 70 *each* cell may contain ~200 genes damaged by such mutations. Such mutations are cumulative and ongoing.

One might consider oneself lucky if the mutations happen to occur in the less than 5% of genes involved in regulating cell division, cell migration, etc. that are involved in cancer development and progression since it could be a relatively rapid progression to death rather than the slow decline of aging as ones genome in each cell gradually decays.

Re:It is not that straightforward

[GospelHead821]

You caught me. I made an ill-informed simplification. Nonetheless, aging, like cancer, would have a relatively small impact on an organism's likelihood to breed. I spoke out of turn when I said there weren't consequences to DNA damage in somatic cells but I think that my conclusion was still reasonably accurate.
(Thank you for pointing out where I was wrong, though. I'm fairly novice at biology but it's a subject I enjoy learning more about.)

The day if the Trifods

[flyingfsck]

Uhmm, would that work on human beings or only on walking and talking plants?

Re:The day if the Trifods

[Thanshin]

Well, you'd have to first turn the subject into plants, then apply the product, and then turn the subject back into human.

A cheaper option is to simply turn a plan you love into a sun-damage-free human.

As always.

Isn't that...

[Chrisq]

Researchers have long known that mammals, including humans, lack a key enzyme ... a sunscreen containing photolyase could potentially heal some of the damage from UV rays that get through.

Isn't that how the lizzardman got started?

there's plenty of cancer to go around

[kronosopher]

Normal sunscreen lotions cause cancer

There, fix'd that for you.

Interpretation of TFA

[kurokame]

IMO the summary is a bit vague on certain points. This sort of gives the impression that the enzyme is restoring "lost data" which was corrupted by exposure to UV, which would amount to dark sorcery.

To get a bit more specific, what seems to be happening from TFA is that the UV dumps some unexpected energy into the DNA (things like light frequency, energy level, time distribution, and so forth probably play a part). This causes the DNA to fold up in order to store the received energy, and it binds to itself in a way it's not supposed to. When transcription or whatever occurs, the normal processes do their thing but aren't aware that the UV light has secretly substituted their normal DNA storage for something which is connected to itself in ways it shouldn't be. The enzyme acts as a catalyst to break these "bad" bonds, which are presumably characteristically different than the "good" bonds which make up the DNA molecule's structure, and probably weaker as well. Therefore the enzyme can break up the "bad" bonds so that the normal cellular processes get what they expect without the enzyme itself posing a risk to the DNA.

Short and simple version: the UV light makes the DNA get tangled up in ways it shouldn't like a user playing with cables, and the enzyme untangles this mess so that the cellular processes can actually find which cord goes where.

Proteins from lotion into skin cells?!

[piotru]

"A sunscreen containing photolyase could potentially heal some of the damage from UV rays that get through"

Genial! Let's extend this method to feeding the beef proteins by massaging meat into the skin!

But, why do we miss this?

[someone1234]

This doesn't sound like intelligent design, nor an evolutionary advantage.
So, why???

Re:But, why do we miss this?

[JamesP]

Because...

If there's no evolutionary pressure on a feature, either way, then it can either stay or disappear.

Re:But, why do we miss this?

[ceoyoyo]

It's God punishing you for your sins. On purpose.

(there's a reasonable discussion of genetic drift and subterranean mammals a few threads above)

Re:the real hazard of sunscreen

[somersault]

Except if you are in the sun a lot (ie enough to get burned), you probably should be using sunscreen otherwise you will get cancer even more quickly, and you're probably getting enough vitamin D in that case anyway (though I have no evidence to back this up).

Re:the real hazard of sunscreen

[Anonymous Coward]

Caucasians got their white skin so they could get enough vitamin D in the places like northern europe.
if you're skin gets burned you received much more sunlight then your skin was evolved to handle. that means you probably produced enough vitamin D in the first hour to last you for the rest of the day.

also using sunscreen doesn't block all the sunlight, just reduces it to more manageable levels. more like what's found in say northern Europe.

Ohio University Press Release is Misleading

[CuteSteveJobs]

> Researchers have long known that mammals, including humans, lack a key enzyme -- one possessed by most of the animal kingdom and even plants -- that reverses severe sun damage

The story description is misleading. By careful omission it gives the impression that this enzyme is the only one that can repair sun-damaged DNA damaged by UV, emphasizing that humans lack it. OH CRUEL LORD! But we do in fact already have other enzymes that repair DNA damage and these are very old news. Ohio U. are just talking about one mechanism, but the press release makes it sound like the only one.

http://en.wikipedia.org/wiki/DNA_repair
http://www.ncbi.nlm.nih.gov/pubmed/8053698

Seems to be a trend with journal articles: Release the journal article and a popular press article; Take huge liberties with the popular press article to guarantee widespread media coverage (and we guess future funding and sunscreen merchandising). Note Ohio U. is the source of the journal article and this press release:
http://www.medicaldaily.com/news/20100725/550/researchers-discover-how-key-enzyme-repairs-sun-damaged-dna.htm

We saw the same thing recently with the silly "chicken or egg" article:
http://www.guardian.co.uk/science/2010/jul/18/chicken-and-egg-conundrum-solved

I'm not knocking either journal article. What they did was pretty cool, but would these people please learn to be honest in their press releases too? You would think they would have learned from Climategate?

Re:Ohio University Press Release is Misleading

[Anonymous Coward]

I love you.

Re:Ohio University Press Release is Misleading

[Aldhibah]

As an alternative to a pernicious media attempting to mislead you, perhaps the problem can be explained by your lack of attention to detail. "Humans do possess some enzymes that can undo damage with less efficiency. But we become sunburned when our DNA is too damaged for those enzymes to repair, and our skin cells die. Scientists have linked chronic sun damage to DNA mutations that lead to diseases such as skin cancer." The article is not about those other enzymes it is about discovering the mechanism by which photolysase works....

Re:Ohio University Press Release is Misleading

[DrLudicrous]

Ohio STATE University. Not Ohio University. There is a huge world of difference. And PR is important, relying on the general media to disseminate information from original scientific journal articles doesn't work. Scientists should be the ones presenting their work, not journalists who are at best mildly fluent in the research areas they cover.

Re:Ohio University Press Release is Misleading

[ceoyoyo]

If you read the actual article, written by a journalist and all, it mentions that this isn't the only DNA repair mechanism, that we do in fact have some other ones, but that this one is particularly effective.

Some other articles on that site

[EmagGeek]

"Nine natural foods to enhance libido"
"Eight instant benefits of meditation"
"Five major health benefits of flax seed"
"Five Yogic cures for respiratory ailments"

Re:Some other articles on that site

[Chrisq]

"Nine natural foods to enhance libido"
"Eight instant benefits of meditation"
"Five major health benefits of flax seed"
"Five Yogic cures for respiratory ailments"

And a partridge in a pear tree

Re:Some other articles on that site

[mcgrew]

You seem to be as ignorant of yoga and meditation as I am of ways to enhance libido and the benefits of flax seed. I was prescribed Hatha Yoga by a medical doctor back in 1975 for arthritis (hatha yoga stretches the joints), and I found that hatha yoga and prana yoga will indeed get rid of a lingering cough after the flu or a cold. I don't remember the name of the yoga that involves meditation, but I assure you that there are many, many benefits. You might want to look at some research on yoga and meditation before dismissing them out of hand.

As I said, I have no idea whether the other two articles are useful or bullshit, but without actually reading the articles you mentioned I'm pretty confident that the two about yoga are not, in fact, bullshit.

Re:the real hazard of sunscreen

[priegog]

Oh no. Not this armchair doctor thing again.
* Vitamin D is NOT "the anti-cancer vitamin" It's a molecule that serves as a hormone to regulate calcium metabolism. It also happens to seem to help prevent some types of cancer, due to semi-related processes. But AFAIK, it has only DEMONSTRATED to reduce the incidence of colon cancer. For skin cancer, it has only been suggested.
* In developed nations, most of us get way more vitamin D from enriched foods and such than we need. So there is no need to go jumping through hoops to get it. Specially hoops that involve you being exposed to a PROVEN carcinogenic (the sun). And even if you somehow DON'T want to believe we get enough vitamin D as-is, remember that to get your daily dose of vitamin D, you only need to expose your forearms (or the equivalent amount of skin) to th sun for 10 minutes. So trust me, even if you wear tons of sunblock, and spend your day under an umbrella, you WILL be getting more than enough vitamin D that way. Heck, you'll get it in the driving up to the beach before you even see the sea.
* Melanoma (the most deadly form of skin cancer, and definitely right up there amongst the deadliest forms of cancer) is associated with repeated ACUTE sunburns (specially in childhood and early adulthood). Basaliomas and epitheliomas are amongst the most common forms of ANY cancer, and are not very deadly. In fact, when found, they often only need to be removed to treat them. These kinds of cancer are (proven, and causally at that) associated with CHRONIC sun exposure. Every little bit of sun counts for this one, as it has a cumulative effect.
* Because of all of this, I think it is pretty stupid to recommend NOT to use sunblock (which would effectively be turning an acute sunburn into a minor exposure), specially when the reason is so that "you can synthetize more of the anti-cancer vitamin". It is also stupid to suggest that everything can be fixed by "taking a vitamin C dose after a sunburn". Where on earth did you get that from? What studies is this claim based on?

This is not to say, things wouldn't be better if people actually used sunblock correctly, or if instead of going to the beach you simply stayed in your mom's basement. But alas, IRL sometimes you need to go the beach to have a little social life. And when you do, you should wear sunblock. Even if you do so incorrectly, some is better than nothing, and even SUGGESTING you should forgo it completely in favor of taking some random pills hoping to cancel out cell damage is stupid, naive, and just irresponsible. I do agree that wearing hats, and long sleeves > sunscreen, but they are not mutually exclusive, you know... and then again, as I said, sometimes you go to the beach to have a good (semi-naked) fun time, not to go hide under a rock.

So please just keep your pseudoscience and personal choices to yourself. Or at least don't recommend people do the same. It's just stupid.

I certainly do not want...

[Wdi]

a sunscreen with enough chemicals added to allow any photolyase molecules from the lotion to permeate into my damaged skin cells.

Any large proteins just slapped onto the skin just stay there, and have no perceivable effect (assuming absence of active transport mechanisms, attack to the cell membrane, etc., which I can confidently exclude in this case).

If you add permeation helpers to destabilize the skin cell membranes sufficiently to allow uptake into the cells, the stuff gets so nasty that any positive effects will certainly far be outweighed by negative side effects.

Re:I certainly do not want...

[cinnamon colbert]

right on the idea that an enzyme like photolyase, applied externally, would do some good, reveals a level of ignorance about basic biochemistry that is frightening I don't suppose that anyone has mentioned that sunblock chemicals, which are tested by the australians, probably are made now in China, and has anyone looked at the quality of htese chemicals, to see if there are harmfull contaminants ?

Binds to your DNA

[goombah99]

Yes it will selll like hotcakes in sun tan lotion once the label says:

BINDS TO YOU DNA
BINDS TO YOUR DNA
or

BINDS AND REARRANGES YOUR DNA!

Good golly, is it possible there is a reason mammals have not re-evolved this?

Re:Binds to your DNA

[maxume]

Yeah, sure. We have fur and don't spend enormous amounts of time in the sun (say, compared to a tree), and the genetic damage mostly doesn't accumulate fast enough to interfere with reproduction.

Somewhat tellingly, we actually have evolved other mechanisms to repair UV-damaged DNA.

Re:the real hazard of sunscreen

[Chrisq]

Caucasians got their white skin so they could get enough vitamin D in the places like northern europe. if you're skin gets burned you received much more sunlight then your skin was evolved to handle. that means you probably produced enough vitamin D in the first hour to last you for the rest of the day.

also using sunscreen doesn't block all the sunlight, just reduces it to more manageable levels. more like what's found in say northern Europe.

One of the big problems is irregular long exposures. I live in Northern Europe, and farmers, gardeners, etc. have quite a tan but no burn. If an office worker stays out of doors for a bright afternoon after staying covered all winter they will burn badly.

Controlled substance

[John Guilt]

Even though possession of melanin in large enough quantities is not longer a criminal offence, not even in Alabama, it universally is considered as an aggravating factor in any trial or police proceeding (see: treatment of 15-year-old drug users: 'young thug' vs 'young man with a promising future who just made a little mistake').

Re:Controlled substance

[Xabraxas]

Or maybe there is a difference between systemic voter intimidation and a couple of nutjobs standing in front of a polling place. You do realize the idiot with the baton was charged with a crime right? I see race-baiting as a tactic is alive as ever with the right wing.

Amazingly Complex

[PineHall]

I am always blown away at how complex a cell can be and the amazing things that it can do. This is just one more article pointing out the amazing complex machinery at the cell level.

TALE of mammals

[Pseudonymus Bosch]

You got me puzzled for a long time until I realized you meant "tale of mammals" instead of "tail of mammals".

Re:the real hazard of sunscreen

[Wonko the Sane]

In developed nations, most of us get way more vitamin D from enriched foods and such than we need.

That hasn't been entirely proven. Just because we don't get rickets doesn't mean that 400 IU/day is an optimal level.

It seems kind of suspicious that (given sufficient sunlight) your skin will synthesize about 10,000 IU per day and then stop manufacturing it. Depending on the strength of sunlight and your skin color it might only take 20 minutes to generate 10,000 IU.

If we've quite clearly evolved to produce more than order magnitude more vitamin D than the current dietary recommendations it's reasonable to wonder if the recommendations are missing something.

Re:the real hazard of sunscreen

[ceoyoyo]

While I agree with you that the GP is full of it, you're not entirely correct either.

Several studies have shown that people who live at temperate latitudes have lower than recommended serum vitamin D levels, particularly during the winter. Certainly not using sunscreen and going out and getting burned is a bad idea, but there's growing evidence that avoiding all unprotected sun exposure (as seems to be commonly recommended) is also not such a good idea. It seems likely that a reasonable amount of sun exposure, not leading to a burn, is good for you.

Re:the real hazard of sunscreen

[priegog]

Or, you know, you could take a freakin' pill if you're THAT worried about having low vitamin D serum levels...
The rest of us over here in sanetown and commonsenseville reckon that as long as our diets are not based on hot pockets and we go out once in a while we'll be Just Fine ®
And yes, chances are you will NOT get skin cancer if you forget the sunblock now and then, but there are other things one could worry about. Photoaging, for one. EVERY LITTLE BIT counts on that one. So while I'm not as sun-paranoid as my previous comment would suggest, I also don't think that PURPOSEFULLY forgoing protection is a good philosophy.

Re:the real hazard of sunscreen

[snadrus]

PROVEN Cancer causing agent == Sun? What about sunblock? Those "active ingredients" rate worse than the Sun.
Only Zinc Oxide & Titanium Dioxide seem ok b/c those don't "rub in", you stay white & pasty all day. Forget waterproof.

Re:the real hazard of sunscreen

[priegog]

Firstly, I'd like to point out how stupid the notion that "everything in nature MUST have a purpose" is. That is not what Darwin's theory is about at all, and yet people seem to have twisted evolution into some sort of sentient overmind orchestring everything towards some greater good (I'm not only referring to your post, this whole story is full of "well if mammals don't have the enzyme surely there's a reason!". But it's really a phenomenon that happens on almost every /. {and Digg's for that matter} story).
Having said that, allow me to tell you why our (caucasians') skin has such a capacity: Because once upon a time, many thousands of years ago, caucasians actually LIVED on the Caucasus (and north-western Europe and Russia too, for that matter) where in winter, the sun is a VERY scarce resource, so much so that the efficiency of their skins to synthesize vit-D was just barely enough to get by; and therefore, people who couldn't synthesize enough Vit-D to remain healthy wouldn't reproduce and would eventually die off.
End of story.

You can sit and ponder whether the recommended dosages are actually enough, but in all honesty, with all the years we've been using the scientific method as the backbone of medicine, we would have noticed by now if people who consumed larger amounts were living significantly longer (or developed superpowers, or whatever else you can think of)

Re:the real hazard of sunscreen

[priegog]

Please show me a study linking (causally) any of such agents to higher cancer incidencies...
Otherwise just keep your conspiracy theories to yourself (or keep writing the FDA) and make a thicker tinfoil hat.
As for me, I'd very much rather stick with your unproven carcinogens (and that even if they were ever to prove themselves as such, they would have a VERY hard time catching up to the sun in that regard) than with a PROVEN one. It's simply what logic and reason dictate.
Oh and I AM white and pasty. I also had to grow a beard recently because I look so young I had trouble being taken seriously at work. Apparently people don't like being told what to do by a (n apparent) teenager.

Re:the real hazard of sunscreen

[ceoyoyo]

There are likely a lot of other benefits to reasonable sun exposure. You can also get your vitamins from a nice pill instead of eating vegetables - do you suppose it's a good idea to skip the veggies to reduce the risk of getting e. coli?

As for photoaging, if you're that vain that EVERY LITTLE BIT counts, you probably wouldn't mind a little cancer, sleep disorder, MS, whatever, in the pursuit of aging gracefully.

Re:the real hazard of sunscreen

[priegog]

There are likely a lot of other benefits to reasonable sun exposure.

Would you mind enlightening the rest of us mortals? Because nevermind the lack of studies, AFAIK no-one (excepting maybe breatharians) claims any other benefits of sun exposure other than Vitamin D (well, it can temporarily reduce the severity of a couple of skin conditions like psoriasis and acne, but those are fully understood and local effects).
Please don't start making 'analogies' to vegetables that don't make any sense.
Your last sentence there gave me a little insight into your belief system. It seems you are of the kind with an irrational fear of seemingly obscure diseases and for which certain people try to come up with all sorts of theories to explain why for some of them the incidence has been rising. And many of those people are the ones trying to live "as naturally as possible", which mind you, I have no problem with, as long as they don't try to spread their misconceptions amongst the general population. And for some reason these conspiracy theories DO seem to catch on much much quicker than anything sane science demonstrates. Anyways, just try to remember that "back in the good ol' days" when we were hunters-gatherers, a 40 year old was a venerable elderly.
But suffice to say that trying to prevent photoaging doesn't necessarily have anything to do with vanity. As I said in my other post, photoaging and chronic sun exposure go hand in hand with the cumulative damage done to skin cells' DNA, and work their way up towards skin cancer. Just to put your sun loving ideas into perspective, roughly 20% of americans will get some sort of skin cancer. And virtually 100% (as of this moment; hopefully this number will go down since sunscreen was invented in the 70's and has been widely used since the late 80's) of those who get to live to a certain age in some countries like Australia (where there is A LOT of sun and the population is not native) will get actinic keratosis, which are precancerous lesions.
So you go ahead and ignore everything doctors have been telling you for years in favour of insubstantial and ethereal benefits; nature knows what's best for you, right? The rest of us will actually use the advancement of science and physiology understanding to our benefit.