Negative regulation of Gcn4 and Msn2 transcription factors by Srb10 cyclin-dependent kinase.
The budding yeast transcriptional activator Gcn4 is rapidly degraded in an SCF(Cdc4)-dependent manner in vivo. Upon fractionation of yeast extracts to identify factors that mediate Gcn4 ubiquitination, we found that Srb10 phosphorylates Gcn4 and thereby marks it for recognition by SCF(Cdc4) ubiquitin ligase. Srb10 is a physiological regulator of Gcn4 stability because both phosphorylation and turnover of Gcn4 are diminished in srb10 mutants. Gcn4 is almost completely stabilized in srb10Delta pho85Delta cells, or upon mutation of all Srb10 phosphorylation sites within Gcn4, suggesting that the Pho85 and Srb10 cyclin-dependent kinases (CDKs) conspire to limit the accumulation of Gcn4. The multistress response transcriptional regulator Msn2 is also a substrate for Srb10 and is hyperphosphorylated in an Srb10-dependent manner upon heat-stress-induced translocation into the nucleus. Whereas Msn2 is cytoplasmic in resting wild-type cells, its nuclear exclusion is partially compromised in srb10 mutant cells. Srb10 has been shown to repress a subset of genes in vivo, and has been proposed to inhibit transcription via phosphorylation of the C-terminal domain of RNA polymerase II. We propose that Srb10 also inhibits gene expression by promoting the rapid degradation or nuclear export of specific transcription factors. Simultaneous down-regulation of both transcriptional regulatory proteins and RNA polymerase may enhance the potency and specificity of transcriptional inhibition by Srb10.
Chi
Y
Y
Division of Biology, California Institute of Technology, Pasadena 91125, USA.
Huddleston
M J
MJ
Zhang
X
X
Young
R A
RA
Annan
R S
RS
Carr
S A
SA
Deshaies
R J
RJ
D000596:Amino Acids / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism; D003470:Culture Media; D056850:Cyclin-Dependent Kinase 8; D018844:Cyclin-Dependent Kinases / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005656:Fungal Proteins / Q000378:metabolism*; D009154:Mutation; D010453:Peptide Synthases / Q000378:metabolism; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D021122:Protein Subunits; D012319:RNA Polymerase II / Q000378:metabolism; D044843:SKP Cullin F-Box Protein Ligases; D029701:Saccharomyces cerevisiae Proteins; D015534:Trans-Activators / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism*; D014452:Ubiquitins / Q000378:metabolism; D015003:Yeasts / Q000235:genetics / Q000378:metabolism
D000596:Amino Acids; D003470:Culture Media; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; C081935:MSN2 protein, S cerevisiae; D021122:Protein Subunits; D029701:Saccharomyces cerevisiae Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D014452:Ubiquitins; D044843:SKP Cullin F-Box Protein Ligases; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D056850:Cyclin-Dependent Kinase 8; D018844:Cyclin-Dependent Kinases; C058605:PHO85 protein, S cerevisiae; C084210:Kin28 protein kinase, S cerevisiae; C498309:SSN3 protein, S cerevisiae; D012319:RNA Polymerase II; D010453:Peptide Synthases