[URE3] prion propagation is abolished by a mutation of the primary cytosolic Hsp70 of budding yeast

[URE3] and [PSI+] are infectious protein forms of the Saccharomyces cerevisiae Ure2p and Sup35p, respectively. We isolated an allelle of SSA2, the primary cytosolic Hsp70, in a screen for mutants unable to maintain [URE3]. Designated ssa2-10, the mutation results in a leucine substitution for proline 395, a conserved residue of the peptide-binding domain. This allele also unexpectedly destabilizes [URE3] in newly formed heterozygotes: [URE3] is either absent in heterozygotes formed by crossing wildtype [URE3] cells with ssa2-10 mutants, or present and fully stable. SSA2 deletion mutants are weakly capable of maintaining [URE3]. The ssa2-10 allele is compatible with propagation of [PSI+]. However, in combination with a deletion of SSA1, ssa2-10 eliminates the nonsense-suppression phenotype of [PSI+] cells. Copyright (C) 2003 John Wiley Sons, Ltd.