Ssa1 overexpression and [PIN(+)] variants cure [PSI(+)] by dilution of aggregates.
Several cellular chaperones have been shown to affect the propagation of the yeast prions [PSI(+)], [PIN(+)] and [URE3]. Ssa1 and Ssa2 are Hsp70 family chaperones that generally cause pro-[PSI(+)] effects, since dominant-negative mutants of Ssa1 or Ssa2 cure [PSI(+)], and overexpression of Ssa1 enhances de novo [PSI(+)] appearance and prevents curing by excess Hsp104. In contrast, Ssa1 was shown to have anti-[URE3] effects, since overexpression of Ssa1 cures [URE3]. Here we show that excess Ssa1 or Ssa2 can also cure [PSI(+)]. This curing is enhanced in the presence of [PIN(+)]. During curing, Sup35-GFP fluorescent aggregates get bigger and fewer in number, which leads to their being diluted out during cell division, a phenotype that was also observed during the curing of [PSI(+)] by certain variants of [PIN(+)]. The sizes of the detergent-resistant [PSI(+)] prion oligomers increase during [PSI(+)] curing by excess Ssa1. Excess Ssa1 likewise leads to an increase in oligomer sizes of low, medium and very high [PIN(+)] variants. While these phenotypes are also caused by inhibition of Hsp104 or Sis1, the overexpression of Ssa1 did not cause any change in Hsp104 or Sis1 levels.
Department of Biological Sciences, University of Illinois at Chicago, 60607, USA.
Vidhu
V
Mathur
Joo Y
JY
Hong
Susan W
SW
Liebman
D000251:Adenosine Triphosphatases / Q000235:genetics / Q000378:metabolism*; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D018628:Gene Dosage; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D010454:Peptide Termination Factors; D011328:Prions / Q000037:antagonists & inhibitors*; D055503:Protein Multimerization; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism*
D005656:Fungal Proteins; D018840:HSP70 Heat-Shock Proteins; D010454:Peptide Termination Factors; D011328:Prions; C542288:SSA2 protein, S cerevisiae; C068068:SUP35 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D000251:Adenosine Triphosphatases; C095973:SSA1 protein, S cerevisiae