Species specificity of ribosomal gene transcription: a factor associated with human RNA polymerase I prevents transcription of mouse rDNA.
An intrinsic property of class I gene transcription by RNA polymerase I (Pol I) is the species specificity of the initiation reaction. Previous studies have demonstrated that species-specific rDNA promoter recognition is brought about by a TBP-TAF complex, termed TIF-IB in mouse and SL1 in man. We have compared the ability of affinity-purified TIF-IB and SL1 to direct transcription from the homologous rDNA template both in a reconstituted transcription system and in nuclear extracts prepared from mouse and human cells. We show that Pol I from both species and the individual transcription factors, with the exception of TIF-IB/SL1, are functionally interchangeable in the reconstituted transcription system containing purified proteins. In nuclear extracts, however, species-specific differences are obvious. Whereas SL1 reprograms a heterologous mouse extract to recognize the human promoter, TIF-IB fails to reprogram a human extract unless it is complemented with mouse Pol I. Crude human, but not mouse, Pol I exhibits species-specific differences that disappear after purification. We propose that in extracts and less purified fractions human Pol I exists as 'holoenzyme' containing associated protein(s) that prevent assembly of TIF-IB-directed initiation complexes at the murine rDNA promoter.
Eberhard
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Division of Molecular Biology of the Cell II, German Cancer Research Center, Heidelberg, Germany.
Grummt
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D000818:Animals; D001685:Biological Factors / Q000502:physiology; D002467:Cell Nucleus / Q000737:chemistry; D002474:Cell-Free System; D004275:DNA, Ribosomal / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000502:physiology*; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D051379:Mice; D035463:Pol1 Transcription Initiation Complex Proteins; D012318:RNA Polymerase I / Q000378:metabolism*; D012335:RNA, Ribosomal / Q000096:biosynthesis* / Q000235:genetics; D013045:Species Specificity; D014157:Transcription Factors / Q000502:physiology*; D014158:Transcription, Genetic
D001685:Biological Factors; D004275:DNA, Ribosomal; D004268:DNA-Binding Proteins; D035463:Pol1 Transcription Initiation Complex Proteins; D012335:RNA, Ribosomal; D014157:Transcription Factors; C063660:transcription initiation factor TIF-IB; D012318:RNA Polymerase I