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Prions, Darwin's Friend
blamanj writes "Prions, the recently discovered bits of protein thought to be responsible for mad cow disease are turning up all over. It has been shown that prions change the behavior of yeasts, and may therefore offer a speedy way for yeast to evolve."
Super beer! Man, for once all this science mumbojumbo actually pays off!
=Smidge=
If only the Selfish Protein knew how much pain it's causing mankind.
Somebody call Dawkins. I smell another book.
...from DNA methylation effecting cell differentiation and cloning and cancer to this new possible epigenetic mechanism for coping with environmental stresses. It doesn't live in the DNA sequence it lives in the runtime. How much more really cool stuff will be found that may be driven by the DNA or the puzzle pieces may be sequenced by it, but doesn't exist "on paper."
Except that these prions are not at all related to the Mad cow disease ones. "Prion" is a class of infectious substance, akin to "bacterium" or "virus". It's a relatively new class, so the mad cow disease ones are best known, but saying "Yeast prions will give you vCJD" is like saying "plant bacteria will give you tuberculosis".
This is interesting for a number of reasons, but the one that sticks out in my mind is the transfer of plasmids between prokaryotes. Eukaryotes, like eyu and me, don't pass our DNA around as casually as, say, Staphlococcus Aureus does. This has the benefit that our DNA is relatively stable, meaning that we are almost guaranteed to be able to breed with someone two or three generations younger than we are ourselves (hellOOOO, Hef!) but the trade-off is that we're not very responsive to environmental stressors that require quick adaptation to survive.
In simpler terms, through conjugation live bacteria can pick up spare DNA from other living bacteria and immediately "evolve" to meet a new environmental challenge without needing to wait for another generation to be born before the mutation can take effect. The plasmid DNA is then passed along to the daughter cells of successuful bacteria. This obviously confers huge selective advantages on bacteria which pick up plasmids that code for antibiotic resistance genes.
I interpret this prion research in yeast to suggest that yeast can experience the same kind of variable protein expression as bacteria, throught the mechanism of prion inactivation. This is significant because eukaryotic cells do not experience conjugation, and generally do not have plasmids, but DO transport various small proteins across the cell wall and into the cytoplasm.
And if it works for yeast, perhaps the prion mechanism is intended to perform the same function in humans, or in the cows that end up with BSE. The test would be to find some gene in a higher mammal that expresses one way when a prion is in conformation A, but expresses another way in conformation B...
Humpty Dumpty was pushed.
It was so bad, that from looking at mitochondrial DNA it looks like we are all descend from a one woman.
_Every_ animal and plant species trivially descends from one individual (counted as females from mitochondrial DNA for simplicity, but it holds for the "real" DNA as well). Nothing strange about it.
What makes our recent past interesting is that the youngest common ancestor is a lot younger than the species. That can indicate a population crunch - though it is not proof of it by any means.
A speciation event would look just the same, for instance - a separate subgroup splits off and grows to dominate, while the original species dies off. Of course, nobody would see it as a speciation event until enough time has passed for the distinct groups to actually differ enough to no longer be able to interbreed.
Trust the Computer. The Computer is your friend.
Speaking as a biologist with research interests in molecular genetics (mutation specifically) and who spent a good deal of time working in a yeast lab this is just fucking amazing. There is a great deal of potential in this.
If prions are acting as a form of epigenetic plasmids then... wow. I mean, just wow. The sheer possibility for customized prions for gene therapy in somatic eukaryotic cells could be huge.
In this light, the mechanism of yeast prion action is more akin to some error prone repair and replication mechanisms in bacteria, which are triggered by stress and result in an increase in spontaneous mutations. This is different from plasmid transfer, which is a directed transfer of well-defined genetic information
In case of mammalian prions, I see no indication of a similar mechanism. Human prion protein huPrP is a cell surface protein which does not interfere with the translation apparatus or with genetic processes in the nucleus. It rather appears to be involved in regulatory processes which transduce signals from outside into the cell.
Yeast and mammalian prions share no common characteristics except for the ability to exist in to different conformations and to autocatalytically propagate one of these conformations. In general, prions are no functionally homogenous group. Another example would be the prions of slime molds, which play a role in the exchange of genetic information by cell fusion. Here the prion-conversion mechanism creates some kind of incompatibility groups, shutting down the fusion zone if two cells belonging to different compatibility groups try to fuse.
The prion phenomenon is a basic biophysical characteristic, it has not to be bound to a certain function. The fact that yeasts and fungi have found a way to use this physical property of certain proteins does not implicate that other prions have to have useful functions also. It is absolutely possible that mammalian prions are a purely pathological phenomenon.
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