The cell cycle regulatory factor TAF1 stimulates ribosomal DNA transcription by binding to the activator UBF.

Control of ribosome biogenesis is a potential mechanism for the regulation of cell size during growth, and a key step in regulating ribosome production is ribosomal RNA synthesis by RNA polymerase I (Pol I). In humans, Pol I transcription requires the upstream binding factor UBF and the selectivity factor SL1 ...
to assemble coordinately on the promoter. UBF is an HMG box-containing factor that binds to the rDNA promoter and activates Pol I transcription through its acidic carboxy-terminal tail. Using UBF (284-670) as bait in a yeast two-hybrid screen, we have identified an interaction between UBF and TAF1, a factor involved in the transcription of cell cycle and growth regulatory genes. Coimmunoprecipitation and protein-protein interaction assays confirmed that TAF1 binds to UBF. Confocal microscopy showed that TAF1 colocalizes with UBF in Hela cells, and cell fractionation experiments provided further evidence that a portion of TAF1 is localized in the nucleolus, the organelle devoted to ribosomal DNA transcription. Cotransfection and in vitro transcription assays showed that TAF1 stimulates Pol I transcription in a dosage-dependent manner. Thus, TAF1 may be involved in the coordinate expression of Pol I- and Pol II-transcribed genes required for protein biosynthesis and cell cycle progression.
Mesh Terms:
Animals, Cell Cycle, Cell-Free System, Cells, Cultured, Chromosomal Proteins, Non-Histone, DNA, Ribosomal, Hela Cells, Histone Chaperones, Humans, Mutation, Pol1 Transcription Initiation Complex Proteins, RNA Polymerase I, RNA Polymerase II, Recombinant Proteins, TATA-Binding Protein Associated Factors, Transcription Factor TFIID, Transcription Factors, Transcription, Genetic, Transfection, Two-Hybrid System Techniques
Curr. Biol.
Date: Dec. 23, 2002
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