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Phosphorylation by G 1 ‐specific cdk–cyclin complexes activates the nucleolar transcription factor UBF
Author(s) -
Voit Renate,
Hoffmann Manuela,
Grummt Ingrid
Publication year - 1999
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/18.7.1891
Subject(s) - biology , cyclin dependent kinase , transcription factor , cyclin , phosphorylation , microbiology and biotechnology , transcription (linguistics) , cdk inhibitor , cancer research , cell cycle , cyclin dependent kinase 2 , genetics , protein kinase a , gene , linguistics , philosophy
Transcription of rRNA genes by RNA polymerase I increases following serum stimulation of quiescent NIH 3T3 fibroblasts. To elucidate the mechanism underlying transcriptional activation during progression through the G 1 phase of the cell cycle, we have analyzed the activity and phosphorylation pattern of the nucleolar transcription factor upstream binding factor (UBF). Using a combination of tryptic phosphopeptide mapping and site‐directed mutagenesis, we have identified Ser484 as a direct target for cyclin‐dependent kinase 4 (cdk4)–cyclin D1‐ and cdk2–cyclin E‐directed phosphorylation. Mutation of Ser484 impairs rDNA transcription in vivo and in vitro . The data demonstrate that UBF is regulated in a cell cycle‐dependent manner and suggest a link between G 1 cdks–cyclins, UBF phosphorylation and rDNA transcription activation.