A KINASE-CYCLIN PAIR IN THE RNA-POLYMERASE-II HOLOENZYME

THE RNA polymerase II holoenzyme consists of RNA polymerase II, a subs et of general transcription factors, and regulatory proteins known as SRB proteins(1,2). The genes encoding SRB proteins were isolated as su ppressors of mutations in the RNA polymerase II carboxy-terminal domai n (CTD3,4). The CTD and SRB proteins have been implicated in the respo nse to transcriptional regulators(1-11). 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 indicat es that the SRB10 and SRB11 proteins form a kinase-cyclin pair in the holoenzyme, The SRB10/11 kinase is essential for a normal transcriptio nal response to galactose induction in vivo. Holoenzymes lacking SRB10 /11 kinase function are strikingly deficient in CTD phosphorylation, A lthough defects in the kinase substantially affect transcription in vi vo, 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 kinas e are missing in these systems, These results indicate that the SRB10/ 11 kinase is involved in CTD phosphorylation and suggest that this mod ification has a role in the response to transcriptional regulators in vivo.