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Phosphorylation by casein kinase 2 facilitates rRNA gene transcription by promoting dissociation of TIF-IA from elongating RNA polymerase I.
Molecular and Cellular Biology
The protein kinase casein kinase 2 (CK2) phosphorylates different components of the RNA polymerase I (Pol I) transcription machinery and exerts a positive effect on rRNA gene (rDNA) transcription. Here we show that CK2 phosphorylates the transcription initiation factor TIF-IA at serines 170 and 172 (Ser170/172), and this phosphorylation triggers the release of TIF-IA from Pol I after transcription initiation. Inhibition of Ser170/172 phosphorylation or covalent tethering of TIF-IA to the RPA43 subunit of Pol I inhibits rDNA transcription, leading to perturbation of nucleolar structure and cell cycle arrest. Fluorescence recovery after photobleaching and chromatin immunoprecipitation experiments demonstrate that dissociation of TIF-IA from Pol I is a prerequisite for proper transcription elongation. In support of phosphorylation of TIF-IA switching from the initiation into the elongation phase, dephosphorylation of Ser170/172 by FCP1 facilitates the reassociation of TIF-IA with Pol I, allowing a new round of rDNA transcription. The results reveal a mechanism by which the functional interplay between CK2 and FCP1 sustains multiple rounds of Pol I transcription.
Amino Acid Sequence, Animals, Casein Kinase II/metabolism, Cell Cycle, Cell Nucleolus/metabolism, Cell Proliferation, DNA, Ribosomal/genetics, Humans, Mice, Models, Biological, Molecular Sequence Data, NIH 3T3 Cells, Phosphoprotein Phosphatases/metabolism, Phosphorylation, Phosphoserine/metabolism, Pol1 Transcription Initiation Complex Proteins, Promoter Regions, Genetic/genetics, Protein Binding, RNA Polymerase I/metabolism, RNA Precursors/biosynthesis, RNA, Ribosomal/genetics, Transcription Factors/chemistry, Transcription Factors/metabolism, Transcription, Genetic
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