hRRN3 is essential in the SL1-mediated recruitment of RNA Polymerase I to rRNA gene promoters.
A crucial step in transcription is the recruitment of RNA polymerase to promoters. In the transcription of human rRNA genes by RNA Polymerase I (Pol I), transcription factor SL1 has a role as the essential core promoter binding factor. Little is known about the mechanism by which Pol I is recruited. We provide evidence for an essential role for hRRN3, the human homologue of a yeast Pol I transcription factor, in this process. We find that whereas the bulk of human Pol I complexes (I alpha) are transcriptionally inactive, hRRN3 defines a distinct subpopulation of Pol I complexes (I beta) that supports specific initiation of transcription. Human RRN3 interacts directly with TAF(I)110 and TAF(I)63 of promoter-selectivity factor SL1. Blocking this connection prevents recruitment of Pol I beta to the rDNA promoter. Furthermore, hRRN3 can be found in transcriptionally autonomous Pol I holoenzyme complexes. We conclude that hRRN3 functions to recruit initiation-competent Pol I to rRNA gene promoters. The essential role for hRRN3 in linking Pol I to SL1 suggests a mechanism for growth control of Pol I transcription.
Pubmed ID: 11250903 RIS Download
Binding Sites | Cell Nucleolus | DNA-Binding Proteins | Gene Expression Regulation | Holoenzymes | Humans | Models, Genetic | Pol1 Transcription Initiation Complex Proteins | Promoter Regions, Genetic | Protein Binding | RNA Polymerase I | RNA, Ribosomal | Transcription Factors | Transcription, Genetic