Cyclin-dependent protein kinase and cyclin homologs SSN3 and SSN8 contribute to transcriptional control in yeast.

Abstract

The SSN3 and SSN8 genes of Saccharomyces cerevisiae were identified by mutations that suppress a defect in SNF1, a protein kinase required for release from glucose repression. Mutations in SSN3 and SSN8 also act synergistically with a mutation of the MIG1 repressor protein to relieve glucose repression. We have cloned the SSN3 and SSN8 genes. SSN3 encodes a cyclin-dependent protein kinase (cdk) homolog and is identical to UMES. SSN8 encodes a cyclin homolog 35% identical to human cyclin C. SSN3 and SSN8 fusion proteins interact in the two-hybrid system and coimmunoprecipitate from yeast cell extracts. Using an immune complex assay, we detected protein kinase activity that depends on both SSN3 and SSN8. Thus, the two SSN proteins are likely to function as a cdk-cyclin pair. Genetic analysis indicates that the SSN3-SSN8 complex contributes to transcriptional repression of diversely regulated genes and also affects induction of the GAL] promoter.In the budding yeast Saccharomyces cerevisiae, expression of glucose-repressed genes in response to glucose starvation requires the SNF1 protein-serine/threonine kinase (1). The SNF1 kinase is widely conserved, and its mammalian counterpart, AMP-activated protein kinase, is involved in regulation of lipid metabolism and cellular stress responses (2). In yeast, genetic evidence indicates that one of the functions of SNF1 is to relieve transcriptional repression mediated by the SSN6-TUP1 repressor complex. This complex is tethered to glucose-repressed promoters, including that of SUC2 (encoding invertase), by the DNA-binding protein MIG1 (3-5). Mutations in SSN6 or TUPI completely relieve glucose repression of SUC2 and bypass the requirement for the SNF1 kinase. A migl mutation partially relieves repression, suggesting that other DNA-binding proteins are also involved (6).Mutations in the SSN3 and SSN8 genes were isolated as suppressors of the snfl mutant defect in SUC2 derepression (7). This selection also yielded mutations in six other SSN genes, including MIG1 (= SSNJ) and SSN6. The ssn3 and ssn8 mutations are weak suppressors alone but show strong synergy with migl. Moreover, in strains wild type for SNF1, both ssn3 and ssn8 act synergistically with migl to relieve glucose repression of SUC2 (6). These findings implicate SSN3 and SSN8 in negative regulation of SUC2 expression. Both mutations also cause flocculence.To explore the regulatory roles of SSN3 and SSN8, we have cloned the genes by complementation. Sequence analysis showed homology to the cyclin-dependent protein kinase (cdk) family and cyclin C, respectively. Many protein kinases involved in cell cycle control are composed of a catalytic subunit, the cdk, and an activating/targeting subunit, the cyclin. We present genetic and biochemical evidence that SSN3 and SSN8 constitute a cdk-cyclin pair. Genetic evidence suggests a general role for SSN3-SSN8 in transcriptional control.*

Cyclin D1 Associates with the TBP-associated factor TAFII250 to regulate Sp1-mediated transcription

“…In addition, the cyclin H-CDK7 complex, also termed CAK for cyclin activating kinase, is associated with TFIIH and acts to phosphorylate the carboxy terminal domain (CTD) of the largest subunit of RNA polymerase II to initiate transcriptional elongation (Fisher et al, 1995;Fisher and Morgan, 1994;Makela et al, 1994). Moreover, cyclin C and CDK8 were found to be associated with the RNA polymerase holoenzyme, but the targets for phosphorylation by CDK8 are unknown (Kuchin et al, 1995;Leopold and O'Farrell, 1991;Lew et al, 1991;Tassan et al, 1995). Finally, cyclin A-cdk2 and cyclin E-cdk2 complexes are targeted to certain promoters with E2F sites through association with E2F-p107 and E2F-p130 complexes (Hijmans et al, 1995;Lees et al, 1992;Smith and Nevins, 1995;Vairo et al, 1995;Xu et al, 1994;Zhu et al, 1995a,b).…”

Promoter-dependent Roles for the Srb10 Cyclin-dependent Kinase and the Hda1 Deacetylase in Tup1-mediated Repression inSaccharomyces cerevisiae

“…Tup1-mediated repression has been observed in an in vitro system using a naked DNA template (Herschbach et al, 1994;Redd et al, 1997). In addition, several components of the PolII transcriptional machinery (Rgr1, Sin4, Rox3, Hrs1, and Srbs8-11) have been identified in genetic screens for loss of Tup1-mediated repression (Sakai et al, 1990;Kuchin et al, 1995;Wahi and Johnson, 1995;Song et al, 1996;Carlson, 1997). A few also have been shown to physically interact with the Ssn6 -Tup1 complex (Gromoller and Lehming, 2000; PapamichosChronakis et al, 2000).…”

pch1 +, a Second Essential C-type Cyclin Gene in Schizosaccharomyces pombe

“…At this point we cannot speculate as to whether the Pch1 is a functional homolog of C-type cyclins in higher eukaryotes. Cyclin C Cyclin C 100 33 36 31 18 26 22 18 Pch1 33 100 20 24 19 17 21 13 Srb11 36 20 100 24 21 20 10 16 Cyclin H 31 24 24 100 35 29 14 18 Mcs2 18 19 21 35 100 37 14 17 Ccl1 26 17 20 29 37 100 17 17 Cdc13 18 13 16 18 17 17 18 100 a Sequence identity in the cyclin box was determined by a pairwise alignment (Drosophila cyclin C (22); S. pombe pch1; S. cerevisiae Srb11 (Ssn8) (31,33); Human cyclin H (52); S. pombe mcs2 (18); S. cerevisiae Ccl1 (53); and S. pombe cdc13 (57) complementation of the triple CLN mutant requires high level overexpression and might result from cross-reactivity between the cdc28 kinase and a class of cyclins normally dedicated to transcription. We propose that a similar cross-reaction between highly overexpressed proteins accounts for our recovery of pch1 in the screen for cdc2 interacting factors.…”

“…Snf1, a serine/threonine kinase, is involved in the regulation of glucose-repressed genes (34). SRB10 and SRB11 were shown to be involved in transcriptional repression and activation of a variety of genes in S. cerevisiae (33). CDK8, the associated kinase of cyclin C, shares significant homology with Srb10, although the functional homology between the two complexes is unknown (35,36).…”

“…In S. cerevisiae, the SRB10 and SRB11 genes, which encode a kinase and C-type cyclin, respectively, were isolated as high copy suppressors of a CTD truncation mutant (31). Independently, SRB10 (SSN3) and SRB11 (SSN8) were isolated as suppressors of a snf1 mutation (32,33). Snf1, a serine/threonine kinase, is involved in the regulation of glucose-repressed genes (34).…”