TBP-associated factors interact with DNA and govern species specificity of RNA polymerase I transcription.
Unlike genes transcribed by RNA polymerases II and III, transcription by RNA polymerase I is highly species-specific. Ribosomal promoter selectivity is brought about by a multisubunit transcription factor (SL1/TIF-IB) which consists of the TATA-binding protein (TBP) and three TBP-associated factors (TAFs). To determine the basis for the inability of SL1/TIF-IB to recognize heterologous rDNA, the transcriptional properties and the subunit composition of the murine and the human factor, as well as a chimeric complex containing epitope-tagged human TBP and murine TAFs, have been compared. We show that TBP can be exchanged between the human and mouse factor indicating that the variable N-terminal domain of TBP does not play a significant role in rDNA promoter selectivity. Instead, DNA binding is brought about by the TAFs. UV crosslinking experiments demonstrate that binding to the ribosomal gene promoter is mediated by two TAFs (TAFI48 and TAFI68) which have the same electrophoretic mobility in the human and mouse factor. The largest TAF is different in both species and is suggested to play a role in the species-specific assembly of productive preinitiation complexes. Thus, evolutionary changes of rDNA promoter sequences have been accompanied by changes in specific TAFs.
Rudloff
U
U
Division of Molecular Biology of the Cell II, German Cancer Research Center, Heidelberg.
Eberhard
D
D
Tora
L
L
Stunnenberg
H
H
Grummt
I
I
D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D004275:DNA, Ribosomal / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D015870:Gene Expression; D006801:Humans; D051379:Mice; D008957:Models, Genetic; D008969:Molecular Sequence Data; D035463:Pol1 Transcription Initiation Complex Proteins; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D012318:RNA Polymerase I / Q000378:metabolism*; D012335:RNA, Ribosomal / Q000096:biosynthesis; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013045:Species Specificity; D016385:TATA Box; D035181:TATA-Box Binding Protein; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic / Q000502:physiology; D014466:Ultraviolet Rays
D004275:DNA, Ribosomal; D004268:DNA-Binding Proteins; D035463:Pol1 Transcription Initiation Complex Proteins; D012335:RNA, Ribosomal; D011993:Recombinant Fusion Proteins; D035181:TATA-Box Binding Protein; D014157:Transcription Factors; C063660:transcription initiation factor TIF-IB; D012318:RNA Polymerase I