Fungal prions have been investigated and lead to a deeper understanding of disease-forming mammilian prions.

Prion-like proteins are found naturally in some plants and non-mammalian animals. Some of these are not associated with any disease state and may possibly even have a useful role. . Because of this, scientists reasoned that such proteins could give some sort of evolutionary advantage to their host. This was suggested to be the case in a species of fungus, Podospora anserina. Genetically compatible colonies of this fungus can merge together and share cellular contents such as nutrients and cytoplasm. A natural system of protective "incompatibility" proteins exists to prevent promiscuous sharing between unrelated colonies. One such protein, called HET-S, adopts a prion-like form in order to function properly . The prion form of HET-S spreads rapidly throughout the cellular network of a colony and can convert the non-prion form of the protein to a prion state after compatible colonies have merged . However, when an incompatible colony tries to merge with a prion-containing colony, the prion causes the "invader" cells to die, ensuring that only related colonies obtain the benefit of sharing resources.

Sup35p & Ure2p

In 1965, Brian Cox, a geneticist working with the yeast Saccharomyces cerevisiae, described a genetic trait (termed with an unusual pattern of inheritance. Despite many years of effort, Cox could not identify a conventional mutation that was responsible for the Reed Wickner correctly hypothesized that ^*" target="_blank" >as well as another mysterious heritable trait, heat shock proteins (which help other proteins fold properly) were intimately tied to the inheritance and transmission of ^*" target="_blank" >and many other yeast prions. Since then, researchers have unravelled how the proteins that code for ^*" target="_blank" >can convert between prion and non-prion forms, as well as the consequences of having intracellular prions. When exposed to certain adverse conditions, evolutionary selection . It has been speculated that the ability to convert between prion infected and prion-free forms enables yeast to quickly and reversibly adapt in variable environments. Nevertheless, Wickner maintains that ^*" target="_blank" >and [PSI+ are diseases .

Classification

As of 2003, the following proteins in Saccharomyces cerevisiae had been identified or postulated as prions:

• Sup35p, forming the ^* element;
• Ure2p, forming the ^* element;
• Rnq1p, forming the element (also known as [PIN+)
• A fifth prion protein, forming the ^* element remains to be identified.

References

1. A census of glutamine/asparagine-rich regions: Implications for their conserved function and the prediction of novel prions. PNAS USA. 2000 Oct 24; 97(22): 11910-5 Free text
2. The protein product of the het-s heterokaryon incompatibility gene of the fungus Podospora anserina behaves as a prion analog. PNAS USA. 1997 Sep 2; 94(18): 9773-8 Free text
3. Amyloid aggregates of the HET-S prionprotein are infectious. PNAS USA. 2002 May 28; 99(11): 7402-7 Free text
4. as an altered URE2 protein: evidence for a prion analog in Saccharomyces cerevisiae. Science. 1994 Apr 22; 264(5158): 566-9 [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=7909170&query_hl=26 Abstract
5. A yeast prion provides a mechanism for genetic variation and phenotypic diversity. Nature. 2000 Sep 28; 407(6803): 477-83 Abstract
6. A small reservoir of disabled ORFs in the yeast genome and its implications for the dynamics of proteome evolution. J Mol Biol. 2002 Feb 22; 316(3): 409-19 Abstract
7. Yeast prions and [PSI⁺ are diseases. PNAS USA. 2005 July 26; 102(30): 10575-80 Free text

See also

• Prion
• Sup35p
• Epigenetics

Biochemistry | Genetics | Prions | Proteins