RAC, A Stable Ribosome-Associated Complex in Yeast Formed by the DnaK-DnaJ Homologs Ssz1p and Zuotin

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 98; no. 7; pp. 3762 - 3767
• Main Authors: Gautschi, Matthias, Lilie, Hauke, Fünfschilling, Ursula, Mun, Andrej, Ross, Suzanne, Lithgow, Trevor, Rücknagel, Peter, Rospert, Sabine
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 27-03-2001; National Acad Sciences; The National Academy of Sciences
• Subjects: Antibodies; Biochemistry; Biological Sciences; Cells; Cytosol; Cytosol - physiology; Dimerization; DNA-Binding Proteins - analysis; DNA-Binding Proteins - chemistry; DNA-Binding Proteins - isolation & purification; DNA-Binding Proteins - physiology; Escherichia coli Proteins; Fungal Proteins - analysis; Fungal Proteins - chemistry; Fungal Proteins - isolation & purification; Fungal Proteins - physiology; Heat-Shock Proteins - chemistry; HSP40 Heat-Shock Proteins; HSP70 Heat-Shock Proteins - chemistry; Mitochondria; Molecular Chaperones - analysis; Molecular Chaperones - physiology; Phenotypes; Protein precursors; Protein transport; Proteins; ribosome-associated complex; Ribosomes; Saccharomyces cerevisiae; Saccharomyces cerevisiae - chemistry; Saccharomyces cerevisiae - physiology; Saccharomyces cerevisiae Proteins; Salts; Ssz1 protein; Yeast; Yeasts; zuotin
• ISSN: 0027-8424; 1091-6490
• 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 Δssz1 strain, whereas overexpression of Ssz1p did not affect the Δzuo1 strain, suggesting a pivotal function for the DnaJ homolog.