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A dual function for chaperones SSB-RAC and the NAC nascent polypeptide-associated complex on ribosomes.

The yeast Hsp70/40 system SSB-RAC (stress 70 B-ribosome-associated complex) binds to ribosomes and contacts nascent polypeptides to assist cotranslational folding. In this study, we demonstrate that nascent polypeptide-associated complex (NAC), another ribosome-tethered system, is functionally connected to SSB-RAC and the cytosolic Hsp70 network. Simultaneous deletions of genes encoding NAC and SSB caused conditional loss of cell viability under protein-folding stress conditions. Furthermore, NAC mutations revealed genetic interaction with a deletion of Sse1, a nucleotide exchange factor regulating the cytosolic Hsp70 network. Cells lacking SSB or Sse1 showed protein aggregation, which is enhanced by additional loss of NAC; however, these mutants differ in their potential client repertoire. Aggregation of ribosomal proteins and biogenesis factors accompanied by a pronounced deficiency in ribosomal particles and translating ribosomes only occurs in ssbDelta and nacDeltassbDelta cells, suggesting that SSB and NAC control ribosome biogenesis. Thus, SSB-RAC and NAC assist protein folding and likewise have important functions for regulation of ribosome levels. These findings emphasize the concept that ribosome production is coordinated with the protein-folding capacity of ribosome-associated chaperones.

Pubmed ID: 20368618


  • Koplin A
  • Preissler S
  • Ilina Y
  • Koch M
  • Scior A
  • Erhardt M
  • Deuerling E


The Journal of cell biology

Publication Data

April 5, 2010

Associated Grants


Mesh Terms

  • Binding Sites
  • Cytosol
  • HSP70 Heat-Shock Proteins
  • Models, Biological
  • Molecular Chaperones
  • Phenotype
  • Protein Folding
  • Ribosomal Proteins
  • Ribosomes
  • Saccharomyces cerevisiae Proteins