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RNA Polymerase Switch in Transcription of Yeast rDNA: Role of Transcription Factor UAF (Upstream Activation Factor) in Silencing rDNA Transcription by RNA Polymerase II

Loan Vu, Imran Siddiqi, Bum-Soo Lee, Cathleen A. Josaitis and Masayasu Nomura
Proceedings of the National Academy of Sciences of the United States of America
Vol. 96, No. 8 (Apr. 13, 1999), pp. 4390-4395
Stable URL: http://www.jstor.org/stable/47576
Page Count: 6
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
RNA Polymerase Switch in Transcription of Yeast rDNA: Role of Transcription Factor UAF (Upstream Activation Factor) in Silencing rDNA Transcription by RNA Polymerase II
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Abstract

Transcription factor UAF (upstream activation factor) is required for a high level of transcription, but not for basal transcription, of rDNA by RNA polymerase I (Pol I) in the yeast Saccharomyces cerevisiae. RRN9 encodes one of the UAF subunits. We have found that rrn9 deletion mutants grow extremely slowly but give rise to faster growing variants that can grow without intact Pol I, synthesizing rRNA by using RNA polymerase II (Pol II). This change is reversible and does not involve a simple mutation. The two alternative states, one suitable for rDNA transcription by Pol I and the other favoring rDNA transcription by Pol II, are heritable not only in mitosis, but also in meiosis. Thus, S. cerevisiae has an inherent ability to transcribe rDNA by Pol II, but this transcription activity is silenced in normal cells, and UAF plays a key role in this silencing by stabilizing the first state.

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