RNA polymerase I remains intact without subunit exchange through multiple rounds of transcription in Saccharomyces cerevisiae.

Previous experiments using mammalian cells suggested that after each round of transcription, RNA polymerase I (Pol I) dissociates into subunits that leave and reenter the nucleolus as individual subunits, before formation of a new initiation complex. In this study, we show that the size and subunit composition of Pol I ...
did not change significantly when Pol I was not engaged in rRNA transcription, brought about by either the absence of Pol I-specific rDNA template or specific inhibition of the transcription initiation step that requires Rrn3p. In fact, Pol I purified from cells completely lacking rDNA repeats was more active than when purified from wild-type cells in an in vitro transcription system designed to assay active Pol I-Rrn3p complexes. Furthermore, measurements of the exchange of A135 and A190 subunits between preexistent Pol I and newly synthesized Pol I showed that these two largest subunits of Pol I do not disassociate through many rounds of transcription in vivo. Thus, Pol I is not a dynamic protein complex but rather a stable enzyme.
Mesh Terms:
DNA, Fungal, DNA, Ribosomal, Models, Biological, Mutation, Plasmids, Pol1 Transcription Initiation Complex Proteins, Protein Subunits, RNA Polymerase I, Saccharomyces cerevisiae, Saccharomyces cerevisiae Proteins, Transcription, Genetic
Proc. Natl. Acad. Sci. U.S.A.
Date: Oct. 19, 2004
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