A TBP-containing multiprotein complex (TIF-IB) mediates transcription specificity of murine RNA polymerase I.
TIF-IB is a transcription factor which interacts with the mouse ribosomal gene promoter and nucleates the formation of an initiation complex containing RNA polymerase I (Pol I). We have purified this factor to near homogeneity and demonstrate that TIF-IB is a large complex (< 200 kDa) which contains several polypeptides. One of the subunits present in this protein complex is the TATA-binding protein (TBP) as revealed by copurification of TIF-IB activity and TBP over different chromatographic steps including immunoaffinity purification. In addition to TBP, three tightly associated proteins (TAFs-I) with apparent molecular weights of 95, 68, and 48 kDa are contained in this multimeric complex. This subunit composition is similar--but not identical--to the analogous human factor SL1. Depletion of TBP from TIF-IB-containing fractions by immunoprecipitation eliminates TIF-IB activity. Neither TBP alone nor fractions containing other TBP complexes are capable of substituting for TIF-IB activity. Therefore, TIF-IB is a unique complex with Pol I-specific TAFs distinct from other TBP-containing complexes. The identification of TBP as an integral part of the murine rDNA promoter-specific transcription initiation factor extends the previously noted similarity of transcriptional initiation by the three nuclear RNA polymerases and underscores the importance of TAFs in determining promoter specificity.
Eberhard
D
D
Institute of Cell and Tumor Biology, German Cancer Research Center, Heidelberg.
Tora
L
L
Egly
J M
JM
Grummt
I
I
D000818:Animals; D000906:Antibodies / Q000276:immunology; D015153:Blotting, Western; D002853:Chromatography, Liquid; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors / Q000276:immunology / Q000302:isolation & purification / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D006367:HeLa Cells; D006358:Hot Temperature; D006801:Humans; D051379:Mice; D035463:Pol1 Transcription Initiation Complex Proteins; D012318:RNA Polymerase I / Q000378:metabolism*; D016385:TATA Box; D035181:TATA-Box Binding Protein; D014157:Transcription Factors / Q000037:antagonists & inhibitors / Q000276:immunology / Q000302:isolation & purification / Q000378:metabolism*; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
D000906:Antibodies; D004268:DNA-Binding Proteins; D035463:Pol1 Transcription Initiation Complex Proteins; D035181:TATA-Box Binding Protein; D014157:Transcription Factors; C063660:transcription initiation factor TIF-IB; D012318:RNA Polymerase I