TTF-I determines the chromatin architecture of the active rDNA promoter.
Transcription of ribosomal genes assembled into chromatin requires binding of the transcription termination factor TTF-I to the promoter-proximal terminator T0. To analyze the mechanism of TTF-I-mediated transcriptional activation, we have used mutant templates with altered sequence, polarity and distance of T0 with respect to the transcription start site. Transcription activation by TTF-I is chromatin specific and requires the precise positioning of the terminator relative to the promoter. Whereas termination by TTF-I depends on the correct orientation of a terminator, TTF-I-mediated transcriptional activation is orientation independent. TTF-I can bind to nucleosomal DNA in the absence of enzymatic activities that destabilize nucleosome structure. Chromatin-bound TTF-I synergizes with ATP-dependent cofactors present in extracts of Drosophila embryos and mouse cells to position a nucleosome over the rDNA promoter and the transcription start site. Nucleosome positioning correlates tightly with the activation of rDNA transcription. We suggest that transcriptional activation by TTF-I is a stepwise process involving the creation of a defined promoter architecture and that the positioning of a nucleosome is compatible with, if not a prerequisite for, transcription initiation from rDNA chromatin.
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German Cancer Research Center, Division of Molecular Biology of the Cell II, Im Neuenheimer Feld 280, 69120 Heidelberg, Germany.
Becker
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D000255:Adenosine Triphosphate / Q000502:physiology; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D002474:Cell-Free System; D002843:Chromatin / Q000235:genetics* / Q000378:metabolism; D018388:Codon, Terminator / Q000502:physiology; D004247:DNA / Q000378:metabolism; D004256:DNA Polymerase I / Q000235:genetics; D004275:DNA, Ribosomal / Q000235:genetics* / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D004330:Drosophila / Q000196:embryology / Q000235:genetics / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D009707:Nucleosomes / Q000235:genetics / Q000378:metabolism; D010443:Peptide Chain Termination, Translational / Q000235:genetics; D011401:Promoter Regions, Genetic; D011485:Protein Binding / Q000235:genetics; D012318:RNA Polymerase I / Q000235:genetics; D014157:Transcription Factors; D015533:Transcriptional Activation
D002843:Chromatin; D018388:Codon, Terminator; D004275:DNA, Ribosomal; D004268:DNA-Binding Proteins; D009707:Nucleosomes; C504003:TTF1 protein, human; D014157:Transcription Factors; C504004:Ttf1 protein, mouse; D000255:Adenosine Triphosphate; D004247:DNA; D012318:RNA Polymerase I; D004256:DNA Polymerase I