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

作者：Koplin Ansgar; Preissler Steffen; Ilina Yulia; Koch Miriam; Scior Annika; Erhardt Marc; Deuerling Elke^*

来源：The Journal of Cell Biology, 2010, 189(1): 57-U86.

DOI：10.1083/jcb.200910074

The yeast Hsp70/40 system SSB-RAC (stress 70 B-ribosome-associated complex) binds to ribosomes and contacts nascent polypeptides to assist coiranslational 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 ssb Delta and nac Delta ssb Delta 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.

• 出版日期2010-4-5