Hsp70 independent role of nucleotide exchange factor Fes1 in degradation of gluconeogenic enzymes and cell wall integrity

Authors

• S Kumar
• DC Masison

Abstract

Hsp70-nucleotide exchange factor (NEF) Fes1 is important for cell growth at high temperature, proteasomal protein degradation, prion propagation, and stress response attenuation. All known functions of Fes1 are thought to require its ability to regulate Hsp70. Here we find Fes1 is essential for vacuole import and degradation (Vid) of gluconeogenic enzymes. We also find Fes1 mutants that do not properly interact with or regulate Hsp70 still retain activities that allow them to support Vid and growth under various stresses. Fes1 bound to Vid substrate Fbp1 in vitro and captured Slt2, a cell wall integrity (CWI) signaling kinase important for high temperature growth, from cell lysates. A Fes1 mutant that does not bind Hsp70 still bound Fbp1 and regulated Slt2 phosphorylation. Our findings reveal that Fes1 binds proteins other than Hsp70, that important cellular functions of Fes1 are independent of it acting as a regulator of Hsp70, and that major growth defects caused by depleting Fes1 are due to loss of these functions rather than to loss of Fes1 regulation of Hsp70.

Scientific Focus Area: Molecular Biology and Biochemistry

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