Mechanistic analysis of RNA polymerase III regulation by the retinoblastoma protein.
The tumour suppressor protein RB restricts cellular growth. This may involve inhibiting the synthesis of tRNA and 5S rRNA by RNA polymerase (pol) III. We have shown previously that RB can repress pol III transcription when overexpressed either in vitro or in vivo. We also demonstrated that pol III activity is elevated substantially in primary fibroblasts from RB-deficient mice. Here we address the molecular mechanism of this regulation. RB is shown to repress all types of pol III promoter. It can do this even if added after transcription complex assembly. Functional assays demonstrate that RB targets specifically the general pol III factor TFIIIB. A physical interaction between TFIIIB and RB is indicated by fractionation, pull-down and immunoprecipitation data. We show that TFIIIB activity is elevated in primary fibroblasts from RB-deficient mice. TFIIIB is a multisubunit complex that includes the TATA-binding protein (TBP) and a TFIIB-related factor called BRF. We show that RB itself contains regions of homology to both TBP and BRF and propose a model in which RB disrupts TFIIIB by mimicking these two components.
Larminie
C G
CG
Institute of Biomedical and Life Sciences, Division of Biochemistry and Molecular Biology, University of Glasgow, UK.
Cairns
C A
CA
Mital
R
R
Martin
K
K
Kouzarides
T
T
Jackson
S P
SP
White
R J
RJ
D000595:Amino Acid Sequence; D000818:Animals; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000378:metabolism; D005347:Fibroblasts; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D008969:Molecular Sequence Data; D011233:Precipitin Tests; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D012320:RNA Polymerase III / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D016160:Retinoblastoma Protein / Q000378:metabolism* / Q000502:physiology; D029701:Saccharomyces cerevisiae Proteins; D017386:Sequence Homology, Amino Acid; D035381:TATA-Binding Protein Associated Factors; D035181:TATA-Box Binding Protein; D035361:Transcription Factor TFIIIB; D014157:Transcription Factors / Q000378:metabolism; D019474:Transcription Factors, TFIII; D014158:Transcription, Genetic / Q000502:physiology*; D000098832:Transcription Factor TFIIIC
C090956:BRF1 protein, S cerevisiae; C441028:BRF1 protein, human; D004268:DNA-Binding Proteins; D011994:Recombinant Proteins; D016160:Retinoblastoma Protein; D029701:Saccharomyces cerevisiae Proteins; D035381:TATA-Binding Protein Associated Factors; D035181:TATA-Box Binding Protein; D035361:Transcription Factor TFIIIB; D014157:Transcription Factors; D019474:Transcription Factors, TFIII; D000098832:Transcription Factor TFIIIC; D012320:RNA Polymerase III