Channel mutations in Hsp104 hexamer distinctively affect thermotolerance and prion-specific propagation.
The yeast prion [PSI(+)] represents an aggregated state of the translation termination factor Sup35 resulting in the tendency of ribosomes to readthrough stop codons. In this study, we constructed an auxotrophic chromosomal marker, ura3-197 (nonsense allele), applicable to selection for loss of [PSI(+)] to [psi(-)]. Unlike [psi(-)] yeast strains, [PSI(+)] yeast strains exhibit nonsense suppression of the ura3-197 allele and are not viable in the presence of 5-fluoroorotic acid (5-FOA) that is converted to a toxic material by the readthrough product of Ura3. We selected 20 5-FOA-resistant, loss-of-[PSI(+)], mutants spontaneously or by transposon-mediated mutagenesis from ura3-197[PSI(+)] cells. All of the 20 [psi(-)] isolates were affected in Hsp104, a protein-remodelling factor. Although most of them were disabled in a normal Hsp104 function for thermotolerance, three single mutants, L462R, P557L and D704N, remained thermotolerant. Importantly, L462R and D704N also eliminate other yeast prions [URE3] and [PIN(+)], while P557L does not, suggesting that Hsp104 harbours a unique activity to prion propagation independent of its function in thermotolerance. The mutations that are specific to prion propagation are clustered around the lateral channel of the Hsp104 hexamer, suggesting a crucial and specific role of this channel for prion propagation.
Kurahashi
Hiroshi
H
Department of Basic Medical Sciences, Institute of Medical Science, University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan.
Nakamura
Yoshikazu
Y
D000483:Alleles; D015966:Gene Expression Regulation, Fungal / Q000502:physiology*; D006360:Heat-Shock Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism / Q000502:physiology*; D016296:Mutagenesis; D009154:Mutation; D011328:Prions / Q000235:genetics* / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism / Q000502:physiology*; D013696:Temperature
D006360:Heat-Shock Proteins; D011328:Prions; D029701:Saccharomyces cerevisiae Proteins; C070972:HsP104 protein, S cerevisiae