The relationship between visible intracellular aggregates that appear after overexpression of Sup35 and the yeast prion-like elements [PSI(+)] and [PIN(+)].
Overproduced fusions of Sup35 or its prion domain with green fluorescent protein (GFP) have previously been shown to form frequent dots in [PSI(+)] cells. Rare foci seen in [psi(-)] cells were hypothesized to indicate the de novo induction of [PSI(+)] caused by the overproduced prion domain. Here, we describe novel ring-type aggregates that also appear in [psi(-)] cultures upon Sup35 overproduction and show directly that dot and ring aggregates only appear in cells that have become [PSI(+)]. The formation of either type of aggregate requires [PIN(+)], an element needed for the induction of [PSI(+)]. Although aggregates are visible predominantly in stationary-phase cultures, [PSI(+)] induction starts in exponential phase, suggesting that much smaller aggregates can also propagate [PSI(+)]. Such small aggregates are probably present in [PSI(+)] cells and, upon Sup35-GFP overproduction, facilitate the frequent formation of dot aggregates, but only the occasional appearance of ring aggregates. In contrast, rings are very frequent when [PSI(+)] cultures, including those lacking [PIN(+)], are grown in the presence of GuHCl or excess Hsp104 while overexpressing Sup35-GFP. Thus, intermediates formed during [PSI(+)] curing seem to facilitate ring formation. Surprisingly, GuHCl and excess Hsp104, which are known to promote loss of [PSI(+)], did not prevent the de novo induction of [PSI(+)] by excess Sup35 in [psi(-)][PIN(+)] strains.
Zhou
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Laboratory for Molecular Biology, Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL 60607, USA.
Derkatch
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Liebman
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D005656:Fungal Proteins / Q000096:biosynthesis* / Q000235:genetics; D049452:Green Fluorescent Proteins; D019791:Guanidine / Q000494:pharmacology; D006360:Heat-Shock Proteins / Q000096:biosynthesis; D008164:Luminescent Proteins / Q000096:biosynthesis / Q000235:genetics; D010454:Peptide Termination Factors; D011328:Prions / Q000096:biosynthesis*; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000648:ultrastructure*; D029701:Saccharomyces cerevisiae Proteins
D005656:Fungal Proteins; D006360:Heat-Shock Proteins; D008164:Luminescent Proteins; D010454:Peptide Termination Factors; D011328:Prions; D011993:Recombinant Fusion Proteins; C068068:SUP35 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C070972:HsP104 protein, S cerevisiae; D049452:Green Fluorescent Proteins; D019791:Guanidine