RAC, a stable ribosome-associated complex in yeast formed by the DnaK-DnaJ homologs Ssz1p and zuotin

Proc Natl Acad Sci U S A. 2001 Mar 27;98(7):3762-7. doi: 10.1073/pnas.071057198.


The yeast cytosol contains multiple homologs of the DnaK and DnaJ chaperone family. Our current understanding of which homologs functionally interact is incomplete. Zuotin is a DnaJ homolog bound to the yeast ribosome. We have now identified the DnaK homolog Ssz1p/Pdr13p as zuotin's partner chaperone. Zuotin and Ssz1p form a ribosome-associated complex (RAC) that is bound to the ribosome via the zuotin subunit. RAC is unique among the eukaryotic DnaK-DnaJ systems, as the 1:1 complex is stable, even in the presence of ATP or ADP. In vitro, RAC stimulates the translocation of a ribosome-bound mitochondrial precursor protein into mitochondria, providing evidence for its chaperone-like effect on nascent chains. In agreement with the existence of a functional complex, deletion of each RAC subunit resulted in a similar phenotype in vivo. However, overexpression of zuotin partly rescued the growth defect of the Delta ssz1 strain, whereas overexpression of Ssz1p did not affect the Delta zuo1 strain, suggesting a pivotal function for the DnaJ homolog.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cytosol / physiology
  • DNA-Binding Proteins / analysis*
  • DNA-Binding Proteins / chemistry
  • DNA-Binding Proteins / isolation & purification*
  • DNA-Binding Proteins / physiology
  • Dimerization
  • Escherichia coli Proteins*
  • Fungal Proteins / analysis*
  • Fungal Proteins / chemistry
  • Fungal Proteins / isolation & purification*
  • Fungal Proteins / physiology
  • HSP40 Heat-Shock Proteins
  • HSP70 Heat-Shock Proteins / chemistry
  • Heat-Shock Proteins / chemistry
  • Mitochondria
  • Molecular Chaperones / analysis*
  • Molecular Chaperones / physiology
  • Saccharomyces cerevisiae / chemistry*
  • Saccharomyces cerevisiae / physiology
  • Saccharomyces cerevisiae Proteins*


  • DNA-Binding Proteins
  • DnaJ protein, E coli
  • Escherichia coli Proteins
  • Fungal Proteins
  • HSP40 Heat-Shock Proteins
  • HSP70 Heat-Shock Proteins
  • Heat-Shock Proteins
  • Molecular Chaperones
  • SSZ1 protein, S cerevisiae
  • Saccharomyces cerevisiae Proteins
  • ZUO1 protein, S cerevisiae
  • dnaK protein, E coli