title: The cell cycle regulatory factor TAF1 stimulates ribosomal DNA transcription by binding to the activator UBF.
abstract: 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.
authors.affiliation: Department of Molecular Microbiology and Immunology, Keck School of Medicine, University of Southern California, Los Angeles, California 90033, USA.
authors.forename: Chih-Yin
authors.initials: CY
authors.lastname: Lin
authors.forename: JoAnn
authors.initials: J
authors.lastname: Tuan
authors.forename: Pierluigi
authors.initials: P
authors.lastname: Scalia
authors.forename: Tiffany
authors.initials: T
authors.lastname: Bui
authors.forename: Lucio
authors.initials: L
authors.lastname: Comai
mesh_terms: D000818:Animals; D002453:Cell Cycle / Q000502:physiology; D002474:Cell-Free System; D002478:Cells, Cultured; D002868:Chromosomal Proteins, Non-Histone / Q000235:genetics / Q000378:metabolism*; D004275:DNA, Ribosomal / Q000235:genetics* / Q000378:metabolism; D004268:DNA-Binding Proteins; D006367:HeLa Cells; D051548:Histone Acetyltransferases; D056488:Histone Chaperones; D006801:Humans; D009154:Mutation; D035463:Pol1 Transcription Initiation Complex Proteins / Q000235:genetics / Q000378:metabolism*; D012318:RNA Polymerase I / Q000235:genetics / Q000378:metabolism; D012319:RNA Polymerase II / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D035381:TATA-Binding Protein Associated Factors / Q000235:genetics / Q000378:metabolism; D035362:Transcription Factor TFIID / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic / Q000502:physiology; D014162:Transfection; D020798:Two-Hybrid System Techniques
chemical_list: D002868:Chromosomal Proteins, Non-Histone; D004275:DNA, Ribosomal; D004268:DNA-Binding Proteins; D056488:Histone Chaperones; D035463:Pol1 Transcription Initiation Complex Proteins; D011994:Recombinant Proteins; C513473:SET protein, human; D035381:TATA-Binding Protein Associated Factors; D035362:Transcription Factor TFIID; D014157:Transcription Factors; C063844:transcription factor UBF; D051548:Histone Acetyltransferases; C069001:TATA-binding protein associated factor 250 kDa; D012319:RNA Polymerase II; D012318:RNA Polymerase I