TFIIIC determines RNA polymerase III specificity at the TATA-containing yeast U6 promoter.
The gene encoding yeast U6 snRNA that is transcribed by RNA polymerase III (Pol III) contains both a TATA box upstream of the transcription start site and a downstream binding site for the factor TFIIIC. This juxtaposition of elements typical of both Pol II- and Pol III-transcribed genes raises the question of how polymerase specificity is determined. The upstream U6 promoter containing the TATA box and transcription start site was shown previously to be transcribed by Pol III in vitro. We therefore tested whether the upstream promoter of yeast U6 encodes Pol III specificity. One model is that polymerase specificity is conferred by the homologous Pol II and Pol III transcription factors TFIIB and BRF1. However, we found no specificity in the binding of BRF1 or TFIIB to TATA-containing promoters of genes specifically transcribed by Pol III or Pol II. Yeast strains deficient for Pol II or Pol III transcription were employed to examine U6 polymerase specificity in vivo. We find that the U6 upstream promoter is Pol II-specific in vivo and is converted to Pol III specificity by TFIIIC. Thus, preferential recruitment of TFIIIB by TFIIIC probably excludes the Pol II general factors and promotes Pol III transcription, thereby determining polymerase specificity.
Roberts
S
S
Fred Hutchinson Cancer Research Center, Seattle, Washington 98104, USA.
Colbert
T
T
Hahn
S
S
D001483:Base Sequence; D006836:Hydro-Lyases / Q000235:genetics; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides; D011401:Promoter Regions, Genetic; D012320:RNA Polymerase III / Q000378:metabolism*; D017414:Ribonucleoprotein, U4-U6 Small Nuclear / Q000235:genetics*; D012441:Saccharomyces cerevisiae / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins; D013379:Substrate Specificity; D016385:TATA Box; D035361:Transcription Factor TFIIIB; D014157:Transcription Factors / Q000378:metabolism*; D019474:Transcription Factors, TFIII; D014158:Transcription, Genetic; D000098832:Transcription Factor TFIIIC
C090956:BRF1 protein, S cerevisiae; D009838:Oligodeoxyribonucleotides; D017414:Ribonucleoprotein, U4-U6 Small Nuclear; D029701:Saccharomyces cerevisiae Proteins; D035361:Transcription Factor TFIIIB; D014157:Transcription Factors; D019474:Transcription Factors, TFIII; D000098832:Transcription Factor TFIIIC; D012320:RNA Polymerase III; D006836:Hydro-Lyases; C021434:imidazoleglycerolphosphate dehydratase