Abstract
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 G1 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 G1 cdks-cyclins, UBF phosphorylation and rDNA transcription activation.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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3T3 Cells
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Animals
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Binding Sites
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CDC2-CDC28 Kinases*
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Cell Nucleolus / metabolism
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Cyclin D1 / metabolism
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Cyclin E / metabolism
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Cyclin-Dependent Kinase 2
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Cyclin-Dependent Kinase 4
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Cyclin-Dependent Kinases / metabolism*
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Cyclins / metabolism*
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DNA, Ribosomal / genetics
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DNA-Binding Proteins / genetics
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DNA-Binding Proteins / metabolism*
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G1 Phase / genetics
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G1 Phase / physiology*
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Mice
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Mutagenesis, Site-Directed
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Peptide Mapping
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Phosphorylation
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Pol1 Transcription Initiation Complex Proteins*
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Protein Serine-Threonine Kinases / metabolism
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Proto-Oncogene Proteins*
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RNA Precursors / biosynthesis
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Transcription Factors / genetics
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Transcription Factors / metabolism*
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Transcriptional Activation
Substances
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Cyclin E
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Cyclins
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DNA, Ribosomal
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DNA-Binding Proteins
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Pol1 Transcription Initiation Complex Proteins
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Proto-Oncogene Proteins
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RNA Precursors
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Transcription Factors
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transcription factor UBF
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Cyclin D1
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Protein Serine-Threonine Kinases
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CDC2-CDC28 Kinases
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Cdk2 protein, mouse
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Cdk4 protein, mouse
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Cyclin-Dependent Kinase 2
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Cyclin-Dependent Kinase 4
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Cyclin-Dependent Kinases