Cln3 activates G1-specific transcription via phosphorylation of the SBF bound repressor Whi5.
G1-specific transcriptional activation by Cln3/CDK initiates the budding yeast cell cycle. To identify targets of Cln3/CDK, we analyzed the SBF and MBF transcription factor complexes by multidimensional protein interaction technology (MudPIT). Whi5 was identified as a stably bound component of SBF but not MBF. Inactivation of Whi5 leads to premature expression of G1-specific genes and budding, whereas overexpression retards those processes. Whi5 inactivation bypasses the requirement for Cln3 both for transcriptional activation and cell cycle initiation. Whi5 associates with G1-specific promoters via SBF during early G1 phase, then dissociates coincident with transcriptional activation. Dissociation of Whi5 is promoted by Cln3 in vivo. Cln/CDK phosphorylation of Whi5 in vitro promotes its dissociation from SBF complexes. Mutation of putative CDK phosphorylation sites, at least five of which are phosphorylated in vivo, strongly reduces SBF-dependent transcription and delays cell cycle initiation. Like mammalian Rb, Whi5 is a G1-specific transcriptional repressor antagonized by CDK.
de Bruin
Robertus A M
RA
Department of Molecular Biology, 10550 North Torrey Pines Road, La Jolla, California 92037, USA.
McDonald
W Hayes
WH
Kalashnikova
Tatyana I
TI
Yates
John
J
Wittenberg
Curt
C
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D048429:Cell Size; D002843:Chromatin / Q000378:metabolism; D016384:Consensus Sequence; D016213:Cyclins / Q000235:genetics / Q000378:metabolism*; D016193:G1 Phase; D015966:Gene Expression Regulation, Fungal; D008957:Models, Genetic; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011233:Precipitin Tests; D011401:Promoter Regions, Genetic; D012097:Repressor Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D015533:Transcriptional Activation
C079895:CLN3 protein, S cerevisiae; D002843:Chromatin; D016213:Cyclins; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors