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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.'"
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.
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.