ABSTRACT
The amounts of RNA polymerase I (Pol I) and basal rDNA transcription factors were determined in yeast whole cell extracts. A 17-fold excess of Pol I was found compared to the Pol I-specific initiation factors upstream activating factor (UAF) and core factor (CF) which underlines that both initiation factors interact with a minor fraction of Pol I when rDNA transcription is active. Surprisingly, Rrn3p, another Pol I-specific initiation factor, is more abundant in cell lysates than UAF and CF. Our analyses revealed that a large fraction of cellular Rrn3p is not associated with Pol I. However, the amount of initiation-active Rrn3p which forms a stable complex with Pol I corresponds to the levels of UAF and CF which have been shown to bind the promoter. Initiation-active Rrn3p dissociates from the template during or immediately after Pol I has switched from initiation to elongation. Our data support a model in which the elongating Pol I leaves the initiation factors UAF, CF and Rrn3p close by the promoter.
Subject(s)
Pol1 Transcription Initiation Complex Proteins/analysis , RNA Polymerase I/analysis , Transcription Factors/analysis , Transcription, Genetic , DNA, Ribosomal/genetics , DNA-Binding Proteins/analysis , DNA-Binding Proteins/genetics , Pol1 Transcription Initiation Complex Proteins/genetics , Promoter Regions, Genetic , RNA Polymerase I/genetics , Saccharomyces cerevisiae/genetics , Saccharomyces cerevisiae Proteins/analysis , Saccharomyces cerevisiae Proteins/genetics , Transcription Factors/geneticsABSTRACT
TFIIH is a multisubunit protein complex that plays an essential role in nucleotide excision repair and transcription of protein-coding genes. Here, we report that TFIIH is also required for ribosomal RNA synthesis in vivo and in vitro. In yeast, pre-rRNA synthesis is impaired in TFIIH ts strains. In a mouse, part of cellular TFIIH is localized within the nucleolus and is associated with subpopulations of both RNA polymerase I and the basal factor TIF-IB. Transcription systems lacking TFIIH are inactive and exogenous TFIIH restores transcriptional activity. TFIIH is required for productive but not abortive rDNA transcription, implying a postinitiation role in transcription. The results provide a molecular link between RNA polymerase I transcription and transcription-coupled repair of active ribosomal RNA genes.
