A kinase–cyclin pair in the RNA polymerase II holoenzyme

Abstract

The RNA polymerase II holoenzyme consists of RNA polymerase II, a subset of general transcription factors, and regulatory proteins known as SRB proteins. The genes encoding SRB proteins were isolated as suppressors of mutations in the RNA polymerase II carboxy-terminal domain (CTD). The CTD and SRB proteins have been implicated in the response to transcriptional regulators. We report here the isolation of two new SRB genes, SRB10 and SRB11, which encode kinase- and cyclin-like proteins, respectively. Genetic and biochemical evidence indicates that the SRB10 and SRB11 proteins form a kinase-cyclin pair in the holoenzyme. The SRB10/11 kinase is essential for a normal transcriptional response to galactose induction in vivo. Holoenzymes lacking SRB10/11 kinase function are strikingly deficient in CTD phosphorylation. Although defects in the kinase substantially affect transcription in vivo, purified holoenzymes lacking SRB10/11 kinase function do not show defects in defined in vitro transcription systems, suggesting that the factors necessary to elicit the regulatory role of the SRB10/11 kinase are missing in these systems. These results indicate that the SRB10/11 kinase is involved in CTD phosphorylation and suggest that this modification has a role in the response to transcriptional regulators in vivo.

Regulation of RNA polymerase II activity by CTD phosphorylation and cell cycle control

“…CDK8 (yeast SRB10) and its regulatory partner cyclin C (yeast SRB11) were initially isolated in yeast using a genetic screen for suppressors of truncation mutations in the RNAP II CTD (Koleske et al, 1992;Thompson et al, 1993;Koleske and Young, 1994;Liao et al, 1995). The CDK8-cyclin C complex was subsequently shown to be associated with the RNAP II holoenzyme in yeast (Liao et al, 1995) and in mammalian cells (Ossipow et al, 1995;Maldonado et al, 1996).…”

“…CDK8 (yeast SRB10) and its regulatory partner cyclin C (yeast SRB11) were initially isolated in yeast using a genetic screen for suppressors of truncation mutations in the RNAP II CTD (Koleske et al, 1992;Thompson et al, 1993;Koleske and Young, 1994;Liao et al, 1995). The CDK8-cyclin C complex was subsequently shown to be associated with the RNAP II holoenzyme in yeast (Liao et al, 1995) and in mammalian cells (Ossipow et al, 1995;Maldonado et al, 1996). More recently, CDK8 and cyclin C were also identi®ed as components of mammalian mediator-and SRB protein-containing co-activator complexes that can both positively and negatively affect (activated) RNAP II transcription activation in vitro (Sun et al, 1998;Boyer et al, 1999;Gu et al, 1999;Hampsey and Reinberg, 1999;Na È a È r et al, 1999;Rachez et al, 1999;Ryu et al, 1999;Malik and Roeder, 2000).…”

Transcriptional regulation by targeted recruitment of cyclin-dependent CDK9 kinase in vivo

“…Distinct cyclin-dependent kinases have been identi®ed in yeast and mammalian RNA polymerase II (RNAPII) complexes and they are able to phosphorylate the C-terminus domain (CTD) of the large subunit of eukaryotic RNAPII (Liao et al, 1995;Maldonado et al, 1996). Three human CDKs (CDK7, CDK8 and CDK9) appear to regulate transcription by phosphorylating the CTD.…”

The Pho85 kinase, a member of the yeast cyclin‐ dependent kinase (Cdk) family, has a regulation mechanism different from Cdks functioning throughout the cell cycle

“…There also exist other Cdk family members functioning in other cellular events: Ccl1 cyclin-Kin28 kinase (Cismowski et al 1995;Valay et al 1995) and Srb11 cyclin-Srb10 kinase (Liao et al 1995) are involved in the phosphorylation of the Cterminal domain of the largest subunit of RNA polymerase II. Whether these Cdks are involved in cell-cycle regulation is not yet clear, but Pho85p was shown to associate with G 1 -cyclin homologues, including Pcl1p, Pcl2p and Pcl9p (Espinoza et al 1994;Measday et al 1994Measday et al , 1997.…”