RNA polymerase switch in transcription of yeast rDNA: Role of transcription factor UAF (upstream activation factor) in silencing rDNA transcription by RNA polymerase II

RNA polymerase switch in transcription of yeast rDNA: Role of transcription factor UAF (upstream activation factor) in silencing rDNA transcription by RNA polymerase II

Department of Biological Chemistry, University of California, Irvine, CA, 92697-1700

Contributed by Masayasu Nomura

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.

Footnotes

↵ * L.V. and I.S. contributed equally to this work.
↵ † Present address: Advanced BioScience Laboratories–Basic Research Program, National Cancer Institute–Frederick Cancer Research and Development Center, Building 539, Room 153, Frederick, MD 21702-1201.
↵ ‡ To whom reprint requests should be addressed. e-mail: mnomura{at}uci.edu.
ABBREVIATIONS:

UAF,

upstream activation factor;

Pol I,

RNA polymerase I;

Pol II,

RNA polymerase II;

PSW,

polymerase-switched state;

5-FOA,

5-fluoroorotic acid