The zinc ribbon domains of the general transcription factors TFIIB and Brf: conserved functional surfaces but different roles in transcription initiation.
The function of the conserved zinc-binding domains in the related Pol II- and Pol III-specific factors TFIIB and Brf was investigated. Three-dimensional structure modeling and mutagenesis studies indicated that for both factors, the functional surface of the zinc ribbon fold consists of a small conserved patch of residues located on one face of the domain comprised mainly of the second and third antiparallel beta strands. Previous studies have shown that the TFIIB zinc ribbon is essential for recruitment of Pol II into the preinitiation complex. In contrast, Pol III recruitment assays and in vitro transcription demonstrate that the disruption of the Brf zinc ribbon does not lead to a defect in Pol III recruitment but, rather, a defect in open complex formation. Therefore, the same conserved surface of the zinc ribbon domain has been adapted to serve distinct roles in the Pol II and Pol III transcription machinery.
Hahn
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Howard Hughes Medical Institute and Fred Hutchinson Cancer Research Center, Seattle, Washington 98109 USA. shahn@fred.fhcrc.org
Roberts
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D000595:Amino Acid Sequence; D000818:Animals; D004271:DNA, Fungal; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D029701:Saccharomyces cerevisiae Proteins; D017386:Sequence Homology, Amino Acid; D035381:TATA-Binding Protein Associated Factors; D035581:Transcription Factor TFIIB; D035361:Transcription Factor TFIIIB; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D014158:Transcription, Genetic / Q000235:genetics / Q000502:physiology*; D015032:Zinc / Q000378:metabolism*
C090956:BRF1 protein, S cerevisiae; C441028:BRF1 protein, human; D004271:DNA, Fungal; D029701:Saccharomyces cerevisiae Proteins; D035381:TATA-Binding Protein Associated Factors; D035581:Transcription Factor TFIIB; D035361:Transcription Factor TFIIIB; D014157:Transcription Factors; D015032:Zinc