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Mitotic silencing of human rRNA synthesis: inactivation of the promoter selectivity factor SL1 by cdc2/cyclin B‐mediated phosphorylation
Author(s) -
Heix Jutta,
Vente Andreas,
Voit Renate,
Budde Andreja,
Michaelidis Theologos M.,
Grummt Ingrid
Publication year - 1998
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1093/emboj/17.24.7373
Subject(s) - biology , phosphorylation , cyclin dependent kinase 1 , mitosis , microbiology and biotechnology , gene silencing , cyclin b , cyclin b1 , cyclin , biochemistry , cell cycle , gene
We have used a reconstituted cell‐free transcription system to investigate the molecular basis of mitotic repression of RNA polymerase I (pol I) transcription. We demonstrate that SL1, the TBP‐containing promoter‐binding factor, is inactivated by cdc2/cyclin B‐directed phosphorylation, and reactivated by dephosphorylation. Transcriptional inactivation in vitro is accompanied by phosphorylation of two subunits, e.g. TBP and hTAF I 110. To distinguish whether transcriptional repression is due to phosphorylation of TBP, hTAF I 110 or both, SL1 was purified from two HeLa cell lines that express either full‐length or the core domain of TBP only. Both TBP‐TAF I complexes exhibit similar activity and both are repressed at mitosis, indicating that the variable N‐terminal domain which contains multiple target sites for cdc2/cyclin B phosphorylation is dispensable for mitotic repression. Protein–protein interaction studies reveal that mitotic phosphorylation impairs the interaction of SL1 with UBF. The results suggest that phosphorylation of SL1 is used as a molecular switch to prevent pre‐initiation complex formation and to shut down rDNA transcription at mitosis.