A 70-kDa heat shock cognate protein suppresses the defects caused by a proteasome mutation in Saccharomyces cerevisiae.

An allele of mutation in the proteasome subunit gene Y7, y7-1, caused a temperature-sensitive growth in S. cerevisiae. One of the multi-copy suppressor genes for this growth defect was identical to SSB1, which encodes a 70-kDa heat shock cognate protein of the yeast. Introduction of the multi-copy SSB1 gene into the y7-1 mutant cells suppressed defects in the degradation of X-beta-galactosidase (X = Arg or Pro) observed in the mutant cells. Thus, the SSB1 protein, one of the chaperons of the yeast, facilitated intracellular protein degradation.