Modulation of intracellular protein degradation by SSB1-SIS1 chaperon system in yeast S. cerevisiae.
In prokaryotes, DnaK-DnaJ chaperon is involved in the protein degradation catalyzed by proteases La and ClpA/B complex as shown in E. coli. To extend this into eukaryotic cells, we examined the effects of hsp70 genes, SSA1 and SSB1, and DnaJ genes, SIS1 and YDJ1, on the growth of proteasome subunit mutants of the yeast S. cerevisiae. The results identified SSB1 and SIS1 as a pair of chaperon genes specifically involved in efficient protein turnover in the yeast, whose overexpression suppressed the growth defects caused by the proteasome mutations. Moreover, a single amino acid substitution in the putative peptide-binding site of SSB1 protein profoundly enhanced the suppression activity, indicating that the activity is mediated by the peptide-binding activity of this chaperon. Thus SSB1, with its partner DnaJ, SIS1, modulates the efficiency of protein turnover through its chaperon activity.
Ohba
M
M
Mitsubishi-Kasei Institute of Life Sciences, Machida-shi, Tokyo, Japan. masa@libra.ls.m-kagaku.co.jp
D000595:Amino Acid Sequence; D018833:Chaperonins / Q000502:physiology*; D003546:Cysteine Endopeptidases / Q000235:genetics / Q000378:metabolism; D003600:Cytosol / Q000201:enzymology / Q000378:metabolism*; D005656:Fungal Proteins / Q000378:metabolism* / Q000502:physiology*; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins / Q000502:physiology*; D006360:Heat-Shock Proteins; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000235:genetics / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics / Q000502:physiology*; D029701:Saccharomyces cerevisiae Proteins
D005656:Fungal Proteins; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D009097:Multienzyme Complexes; C070320:SIS1 protein, S cerevisiae; C095192:SSB1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D018833:Chaperonins