http://phys.org/news/2012-02-prion-proteins-powerful-role-survival.html#jCp
Prion proteins don’t just cause scary diseases. They are also “commonly used in yeast to produce beneficial traits,” which “can be passed on to subsequent generations and eventually become ‘hard-wired’ into the genome, contributing to evolutionary change.”
Some proteins in yeast spontaneously misfold, altering their function. This alteration produces new heritable traits in the yeast. Before yeast prions were studied, “prions capable of modifying phenotypes ha[d] never been found in nature.” We’ve learned a lot about the damage that protein misfolding can cause in humans, but in the case of yeast, misfolding can be beneficial if the diverse new traits produced in the process help the yeast survive.
I think the following excerpts from the article are especially interesting:
“[T]he rate at which proteins switch into and out of the prion state increases in response to environmental stress [such as high acidity or the presence of antifungal agents], suggesting that they are part of an inherent survival mechanism that helps yeasts adapt to changes in their surroundings.”
Scientists studying prions in wild yeast found that “approximately 40% of the traits produced by the wild prions proved to beneficial to growth…’How frequently beneficial they are suggests that the prions have already been subject to previous, positive selective events,’ says [Susan] Lindquist. ‘We see them as part of a bet-hedging strategy that allows the yeast to alter their biological properties quickly when their environments turn unfavorable.’ Convinced of the impact prions have had on yeast evolution, Lindquist speculates that these shape-shifting proteins may be ‘remnants of early life,’ from a time when inheritance was predominantly protein-based rather than nucleic-acid based. She also theorizes that prions may play such roles beyond yeast, and her lab intends to take similar approaches in the hunt for prion activity in other organisms.”