REPRESSION OF RNA-POLYMERASE-II AND RNA-POLYMERASE-III TRANSCRIPTION DURING M-PHASE OF THE CELL-CYCLE

Nuclear transcription is repressed when eukaryotic cells enter mitosis . Using Xenopus egg extracts shifted to the mitotic state with recombi nant cyclin B1 protein, we have been able to reproduce mitotic repress ion of transcription in vitro. Active RNA polymerase I-II transcriptio n is observed in interphase extracts in the absence of added cy clin, but is strongly repressed by the induction of cdc2/cyclin B (maturatio n/mitosis promoting factor, MPF) kinase activity in the mitotic extrac t. Studies with protein kinase inhibitors show that protein phosphoryl ation is required for repression. Add-back experiments indicate that r epression of class III gene transcription is due to inactivation of th e transcription factor TFIIIB. TFIIIB is composed of the TATA-box bind ing protein (TBP) and TBP-associated factors of 75 and 92 kDa. In the present study, we show that TBP and a polypeptide of 92 kDa are substr ates of the mitotic kinase in highly purified TFIIIB fractions. We als o show that a phosphatase present in the Xenopus egg extract can react ivate transcription after repression by the mitotic kinases. This resu lt suggests a mechanism for reactivation of transcription after exit f rom mitosis into the G1 phase of the cell cycle. As for pol III genes, purified cdc2/cyclin B kinase is sufficient to inhibit, transcription by RNA polymerase II in a reconstituted transcription system containi ng the basal transcription factors and polymerase. (C) 1996 Academic P ress, Inc.