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
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
PubMed ID: 15477604
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