Cytosolic splice isoform of Hsp70 nucleotide exchange factor Fes1 is required for the degradation of misfolded proteins in yeast

Mol Biol Cell. 2016 Apr 15;27(8):1210-9. doi: 10.1091/mbc.E15-10-0697. Epub 2016 Feb 24.


Cells maintain proteostasis by selectively recognizing and targeting misfolded proteins for degradation. InSaccharomyces cerevisiae, the Hsp70 nucleotide exchange factor Fes1 is essential for the degradation of chaperone-associated misfolded proteins by the ubiquitin-proteasome system. Here we show that theFES1transcript undergoes unique 3' alternative splicing that results in two equally active isoforms with alternative C-termini, Fes1L and Fes1S. Fes1L is actively targeted to the nucleus and represents the first identified nuclear Hsp70 nucleotide exchange factor. In contrast, Fes1S localizes to the cytosol and is essential to maintain proteostasis. In the absence of Fes1S, the heat-shock response is constitutively induced at normally nonstressful conditions. Moreover, cells display severe growth defects when elevated temperatures, amino acid analogues, or the ectopic expression of misfolded proteins, induce protein misfolding. Importantly, misfolded proteins are not targeted for degradation by the ubiquitin-proteasome system. These observations support the notion that cytosolic Fes1S maintains proteostasis by supporting the removal of toxic misfolded proteins by proteasomal degradation. This study provides key findings for the understanding of the organization of protein quality control mechanisms in the cytosol and nucleus.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alternative Splicing
  • Cell Nucleus / metabolism
  • Cytosol / metabolism*
  • Gene Expression Regulation, Fungal
  • HSP70 Heat-Shock Proteins / metabolism
  • Heat-Shock Response
  • Intracellular Signaling Peptides and Proteins / genetics*
  • Intracellular Signaling Peptides and Proteins / metabolism*
  • Introns
  • Luciferases, Firefly / chemistry
  • Luciferases, Firefly / metabolism
  • Polyadenylation
  • Promoter Regions, Genetic
  • Proteasome Endopeptidase Complex / metabolism
  • Protein Folding
  • Protein Isoforms
  • Saccharomyces cerevisiae / metabolism
  • Saccharomyces cerevisiae Proteins / genetics*
  • Saccharomyces cerevisiae Proteins / metabolism*
  • Ubiquitin / metabolism


  • FES1 protein, S cerevisiae
  • HSP70 Heat-Shock Proteins
  • Intracellular Signaling Peptides and Proteins
  • Protein Isoforms
  • Saccharomyces cerevisiae Proteins
  • Ubiquitin
  • Luciferases, Firefly
  • Proteasome Endopeptidase Complex