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.
Koplin
Ansgar
A
Laboratory of Molecular Microbiology, Department of Biology, and 2 Konstanz Research School of Chemical Biology, University of Konstanz, 78457 Konstanz, Germany.
Preissler
Steffen
S
Ilina
Yulia
Y
Koch
Miriam
M
Scior
Annika
A
Erhardt
Marc
M
Deuerling
Elke
E
D001665:Binding Sites; D003600:Cytosol / Q000378:metabolism; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D008954:Models, Biological; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism*; D010641:Phenotype; D017510:Protein Folding; D012269:Ribosomal Proteins / Q000235:genetics / Q000378:metabolism*; D012270:Ribosomes / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*
D018840:HSP70 Heat-Shock Proteins; D018832:Molecular Chaperones; D012269:Ribosomal Proteins; D029701:Saccharomyces cerevisiae Proteins; C096099:nascent-polypeptide-associated complex