Are prions an important driver in evolution?

Question

I understand that prions have been implicated in the passing on of epigentic information^[1]. Are prions thought to play a significant role in the evolution of organisms?

1. Alberti S, Halfmann R, King O, Kapila A, Lindquist S. 2009. A systematic survey identifies prions and illuminates sequence features of prionogenic proteins. Cell 137: 146–58.

Answer 1

It is proposed that prions are a good mechanism for "testing" phenotypic variation.

There are many identified proteins with prion-determining domains (PrD) in the yeast genome that can spontaneously switch between conformations with some low probability (eg: check SUP35 for one example, and [1] for a good overview of more). The theory is that:

1. the low probability of switching from non-prion to prion state allows for many more mutations and variations to accumulate -- generating greater genetic diversity than in standard expressed gene variability where most mutations are silent or detrimental
2. the prions provide a ready form of non-permanent inheritability that can be "trialed" by offspring and others in a colony of organisms -- this can be especially beneficial during say temporary changes in environment
3. if the prion phenotype is widely successful, selective pressure can easily mutate it into a more permanent fixture in the genome.

Check out the excellent paper published just last week in Nature exploring this this topic [2]. To give a sense of just how evolutionarily-advantageous prions can be, in the author's experiments and analysis they note that 40% of the prion traits they analyzed were beneficial to growth (eg: in the paper strain UCD939 gains additional resistance to acidic conditions from the prion [PSI+]).

Assuming these hypothesis, prions would thus play a significant role in the evolution and variability of organisms.

[1] Crow, et. al. 2011. doi:10.1016/j.semcdb.2011.03.003

[2] Halfmann, et. al. 2012. doi:10.1038/nature10875

Answer 2

prions were discovered as the mediator of Kuru, a disease gotten from a ritual cannibalism. Its a fatal neural degenerative disease.

I mean I would say that anything that is fatal is a significant evolutionary factor. Now that we can possibly contract it just from eating cow meat as well, I guess you could also say that it is also wide spread.

Does that make it as important in human selection as, owning a nice car or 'spring break'? That's harder to say.

http://en.wikipedia.org/wiki/Kuru_(disease)