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Proteasome‐ and SCF‐dependent degradation of yeast adenine deaminase upon transition from proliferation to quiescence requires a new F‐box protein named Saf1p
Author(s) -
Escusa Stéphanie,
Camblong Jurgi,
Galan JeanMarc,
Pinson Benoît,
DaignanFornier Bertrand
Publication year - 2006
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2006.05153.x
Subject(s) - biology , skp1 , f box protein , proteasome , saccharomyces cerevisiae , cell division control protein 4 , microbiology and biotechnology , protein degradation , ubiquitin ligase , downregulation and upregulation , kinase , gene expression , regulation of gene expression , transcriptional regulation , gene , biochemistry , ubiquitin
Summary In response to nutrient limitation, Saccharomyces cerevisiae cells enter into a non‐proliferating state termed quiescence. This transition is associated with profound changes in gene expression patterns. The adenine deaminase encoding gene AAH1 is among the most precociously and tightly downregulated gene upon entry into quiescence. We show that AAH1 downregulation is not specifically due to glucose exhaustion but is a more general response to nutrient limitation. We also found that Aah1p level is tightly correlated to RAS activity indicating thus an important role for the protein kinase A pathway in this regulation process. We have isolated three deletion mutants, srb10 , srb11 and saf1 ( ybr280c ) affecting AAH1 expression during post‐diauxic growth and in early stationary phase. We show that the Srb10p cyclin‐dependent kinase and its cyclin, Srb11p, regulate AAH1 expression at the transcriptional level. By contrast, Saf1p, a previously uncharacterized F‐box protein, acts at a post‐transcriptional level by promoting degradation of Aah1p. This post‐transcriptional regulation is abolished by mutations affecting the proteasome or constant subunits of the SCF ( S kp1– C ullin– F ‐box) complex. We propose that Saf1p targets Aah1p for proteasome‐dependent degradation upon entry into quiescence. This work provides the first direct evidence for active degradation of proteins in quiescent yeast cells.