A role for cytosolic hsp70 in yeast [PSI(+)] prion propagation and [PSI(+)] as a cellular stress |
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Authors: | Jung G Jones G Wegrzyn R D Masison D C |
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Affiliation: | Laboratory of Biochemistry and Genetics, National Institute of Diabetes, Digestive, and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-0851, USA. |
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Abstract: | [PSI(+)] is a prion (infectious protein) of Sup35p, a subunit of the Saccharomyces cerevisiae translation termination factor. We isolated a dominant allele, SSA1-21, of a gene encoding an Hsp70 chaperone that impairs [PSI(+)] mitotic stability and weakens allosuppression caused by [PSI(+)]. While [PSI(+)] stability is normal in strains lacking SSA1, SSA2, or both, SSA1-21 strains with a deletion of SSA2 cannot propagate [PSI(+)]. SSA1-21 [PSI(+)] strains are hypersensitive to curing of [PSI(+)] by guanidine-hydrochloride and partially cured of [PSI(+)] by rapid induction of the heat-shock response but not by growth at 37 degrees. The number of inheritable [PSI(+)] particles is significantly reduced in SSA1-21 cells. SSA1-21 effects on [PSI(+)] appear to be independent of Hsp104, another stress-inducible protein chaperone known to be involved in [PSI(+)] propagation. We propose that cytosolic Hsp70 is important for the formation of Sup35p polymers characteristic of [PSI(+)] from preexisting material and that Ssa1-21p both lacks and interferes with this activity. We further demonstrate that the negative effect of heat stress on [PSI(+)] phenotype directly correlates with solubility of Sup35p and find that in wild-type strains the presence of [PSI(+)] causes a stress that elevates basal expression of Hsp104 and SSA1. |
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