MITOTIC PHOSPHORYLATION OF THE TBP-CONTAINING FACTOR SL1 REPRESSES RIBOSOMAL GENE-TRANSCRIPTION

Entry into mitosis is accompanied by a global repression of transcript ion. To investigate the molecular mechanisms which shut-down rRNA synt hesis during mitosis, we have compared RNA polymerase I (Pol I) transc ription in extracts from asynchronous and mitotic HeLa cells. We show by several experimental approaches that phosphorylation by cdc2/cyclin B inactivates the TBP-containing factor SL1 and thus abrogates Pol I transcription during mitosis. This finding links the cell's cycle with the transcriptional activity of Pol I and suggests a common mechanism for mitotic silencing of all three classes of nuclear RNA polymerases , i.e. reversible inactivation of the respective TBP-TAF complexes by (a) mitotic kinase(s). (C) 1998 Academic Press.