RAC, a stable ribosome-associated complex in yeast formed by the DnaK-DnaJ homologs Ssz1p and zuotin.
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.
Enzymology of Protein Folding, Max Planck Research Laboratory, Weinbergweg 22, D-06120 Halle/Saale, Germany.
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D003600:Cytosol / Q000502:physiology; D004268:DNA-Binding Proteins / Q000032:analysis* / Q000737:chemistry / Q000302:isolation & purification* / Q000502:physiology; D019281:Dimerization; D029968:Escherichia coli Proteins; D005656:Fungal Proteins / Q000032:analysis* / Q000737:chemistry / Q000302:isolation & purification* / Q000502:physiology; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins / Q000737:chemistry; D006360:Heat-Shock Proteins / Q000737:chemistry; D008928:Mitochondria; D018832:Molecular Chaperones / Q000032:analysis* / Q000502:physiology; D012441:Saccharomyces cerevisiae / Q000737:chemistry* / Q000502:physiology; D029701:Saccharomyces cerevisiae Proteins
D004268:DNA-Binding Proteins; C494635:DnaJ protein, E coli; D029968:Escherichia coli Proteins; D005656:Fungal Proteins; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; C424445:SSZ1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C077019:ZUO1 protein, S cerevisiae; C063842:dnaK protein, E coli