The composition of the RNA polymerase I transcription machinery switches from initiation to elongation mode.
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.
Bier
Mirko
M
Biochemie-Zentrum Heidelberg, Im Neuenheimer Feld 328, D-69120 Heidelberg, Germany.
Fath
Stephan
S
Tschochner
Herbert
H
D004275:DNA, Ribosomal / Q000235:genetics; D004268:DNA-Binding Proteins / Q000032:analysis / Q000235:genetics; D035463:Pol1 Transcription Initiation Complex Proteins / Q000032:analysis* / Q000235:genetics; D011401:Promoter Regions, Genetic; D012318:RNA Polymerase I / Q000032:analysis* / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000032:analysis / Q000235:genetics; D014157:Transcription Factors / Q000032:analysis* / Q000235:genetics; D014158:Transcription, Genetic
D004275:DNA, Ribosomal; D004268:DNA-Binding Proteins; D035463:Pol1 Transcription Initiation Complex Proteins; C101161:RRN3 protein, S cerevisiae; C090311:RRN6 protein, S cerevisiae; C098778:RRN9 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D012318:RNA Polymerase I