Editing Prion (section)

== Fungi ==
{{Main|Fungal prion}}

Proteins showing prion-type behavior are also found in some [[fungus|fungi]], which has been useful in helping to understand mammalian prions. [[Fungal prion]]s do not always cause disease in their hosts.<ref>{{cite journal | vauthors = Lindquist S, Krobitsch S, Li L, Sondheimer N | title = Investigating protein conformation-based inheritance and disease in yeast | journal = Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences | volume = 356 | issue = 1406 | pages = 169–176 | date = February 2001 | pmid = 11260797 | pmc = 1088422 | doi = 10.1098/rstb.2000.0762 }}</ref> In yeast, protein refolding to the prion configuration is assisted by [[Chaperone (protein)|chaperone proteins]] such as [[Hsp104]].<ref name='Aguzzi'>{{cite journal | vauthors = Aguzzi A | title = Unraveling prion strains with cell biology and organic chemistry | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 105 | issue = 1 | pages = 11–12 | date = January 2008 | pmid = 18172195 | pmc = 2224168 | doi = 10.1073/pnas.0710824105 | doi-access = free | bibcode = 2008PNAS..105...11A }}</ref> All known prions induce the formation of an [[amyloid]] fold, in which the protein polymerises into an aggregate consisting of tightly packed [[beta sheet]]s. Amyloid aggregates are fibrils, growing at their ends, and replicate when breakage causes two growing ends to become four growing ends. The [[incubation period]] of prion diseases is determined by the [[exponential growth]] rate associated with prion replication, which is a balance between the linear growth and the breakage of aggregates.<ref name="Masel 99">{{cite journal | vauthors = Masel J, Jansen VA, Nowak MA | title = Quantifying the kinetic parameters of prion replication | journal = Biophysical Chemistry | volume = 77 | issue = 2–3 | pages = 139–152 | date = March 1999 | pmid = 10326247 | doi = 10.1016/S0301-4622(99)00016-2 | citeseerx = 10.1.1.178.8812 }}</ref>

Fungal proteins that exhibit templated structural change were discovered in the yeast ''[[Saccharomyces cerevisiae]]'' by [[Reed Wickner]] in the early 1990s. For their mechanistic similarity to mammalian prions, they were termed [[yeast prion]]s. Subsequent to this, a prion has also been found in the fungus ''[[Podospora anserina]]''. These prions behave similarly to PrP, but, in general, are nontoxic to their hosts. [[Susan Lindquist]]'s group at the [[Whitehead Institute]] has argued some of the fungal prions are not associated with any disease state, but may have a useful role; however, researchers at the NIH have also provided arguments suggesting that fungal prions could be considered a diseased state.<ref>{{cite journal | vauthors = Dong J, Bloom JD, Goncharov V, Chattopadhyay M, Millhauser GL, Lynn DG, Scheibel T, Lindquist S | title = Probing the role of PrP repeats in conformational conversion and amyloid assembly of chimeric yeast prions | journal = The Journal of Biological Chemistry | volume = 282 | issue = 47 | pages = 34204–12 | date = November 2007 | pmid = 17893150 | pmc = 2262835 | doi = 10.1074/jbc.M704952200 | doi-access = free }}</ref> There is evidence that fungal proteins have evolved specific functions that are beneficial to the microorganism that enhance their ability to adapt to their diverse environments.<ref>{{cite journal | vauthors = Newby GA, Lindquist S | title = Blessings in disguise: biological benefits of prion-like mechanisms | journal = Trends in Cell Biology | volume = 23 | issue = 6 | pages = 251–9 | date = June 2013 | pmid = 23485338 | doi = 10.1016/j.tcb.2013.01.007 | hdl-access = free | hdl = 1721.1/103966 }}</ref> Further, within yeasts, prions can act as vectors of [[Epigenetics|epigenetic]] inheritance, transferring traits to offspring without any [[Genome|genomic]] change.<ref>{{cite journal | vauthors = Halfmann R, Lindquist S | title = Epigenetics in the extreme: prions and the inheritance of environmentally acquired traits | journal = Science | volume = 330 | issue = 6004 | pages = 629–632 | date = October 2010 | pmid = 21030648 | doi = 10.1126/science.1191081 | s2cid = 206527151 | bibcode = 2010Sci...330..629H }}</ref><ref>{{cite journal | vauthors = Halfmann R, Jarosz DF, Jones SK, Chang A, Lancaster AK, Lindquist S | title = Prions are a common mechanism for phenotypic inheritance in wild yeasts | journal = Nature | volume = 482 | issue = 7385 | pages = 363–8 | date = February 2012 | pmid = 22337056 | pmc = 3319070 | doi = 10.1038/nature10875 | bibcode = 2012Natur.482..363H }}</ref>

Research into [[fungal prion]]s has given strong support to the protein-only concept, since purified protein extracted from cells with a prion state has been demonstrated to convert the normal form of the protein into a misfolded form ''[[in vitro]]'', and in the process, preserve the information corresponding to different strains of the prion state. It has also shed some light on prion domains, which are regions in a protein that promote the conversion into a prion. Fungal prions have helped to suggest mechanisms of conversion that may apply to all prions, though fungal prions appear distinct from infectious mammalian prions in the lack of cofactor required for propagation. The characteristic prion domains may vary between species&nbsp;– e.g., characteristic fungal prion domains are not found in mammalian prions.{{citation needed|date=January 2023}}

{| class="wikitable"
|+ Fungal prions
|-
! [[Protein]]
! Natural host
! Normal function
! Prion state
! Prion phenotype
! Year identified
|-
| [[Ure2]]p
| ''[[Saccharomyces cerevisiae]]''
| Nitrogen catabolite repressor
| [URE3]
| Growth on poor nitrogen sources
| 1994
|-
| [[Sup35p]]
| ''S. cerevisiae''
| Translation termination factor
| [PSI+]
| Increased levels of nonsense suppression
| 1994
|-
| HET-S
| ''Podospora anserina''
| Regulates [[heterokaryon]] incompatibility
| [Het-s]
| Heterokaryon formation between incompatible strains
|
|-
| Rnq1p
| ''S. cerevisiae''
| Protein template factor
| [RNQ+], [PIN+]
| Promotes aggregation of other prions
|
|-
| Swi1
| ''S. cerevisiae''
| Chromatin remodeling
| [SWI+]
| Poor growth on some carbon sources
| 2008
|-
| Cyc8
| ''S. cerevisiae''
| Transcriptional repressor
| [OCT+]
| Transcriptional derepression of multiple genes
| 2009
|-
| Mot3
| ''S. cerevisiae''
| Nuclear transcription factor
| [MOT3+]
| Transcriptional derepression of anaerobic genes
| 2009
|-
| Sfp1
| ''S. cerevisiae''
| Putative transcription factor
| [ISP+]
| Antisuppression
| 2010<ref name="RogozaT">{{cite journal | vauthors = Rogoza T, Goginashvili A, Rodionova S, Ivanov M, Viktorovskaya O, Rubel A, Volkov K, Mironova L | title = Non-Mendelian determinant [ISP+] in yeast is a nuclear-residing prion form of the global transcriptional regulator Sfp1 | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 107 | issue = 23 | pages = 10573–7 | date = June 2010 | pmid = 20498075 | pmc = 2890785 | doi = 10.1073/pnas.1005949107 | doi-access = free | bibcode = 2010PNAS..10710573R }}</ref>{{contradictory inline|Text did not say about this even as of 2012|date=November 2012}}
|}