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Vol. 17, Issue 4, 1744-1757, April 2006

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Distinct Roles for the Essential MYST Family HAT Esa1p in Transcriptional Silencing

Astrid S. Clarke ^* , Eva Samal  , and Lorraine Pillus ^*

^* Division of Biological Sciences, UCSD Cancer Center and Center for Molecular Genetics, University of California, San Diego, La Jolla, CA 92093; Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093

Submitted July 11, 2005; Revised December 13, 2005; Accepted January 18, 2006
Monitoring Editor: Susan Wente

Among acetyltransferases, the MYST family enzyme Esa1p is distinguished for its essential function and contribution to transcriptional activation and DNA double-stranded break repair. Here we report that Esa1p also plays a key role in silencing RNA polymerase II (Pol II)-transcribed genes at telomeres and within the ribosomal DNA (rDNA) of the nucleolus. These effects are mediated through Esa1p's HAT activity and correlate with changes within the nucleolus. Esa1p is enriched within the rDNA, as is the NAD-dependent protein deacetylase Sir2p, and the acetylation levels of key Esa1p histone targets are reduced in the rDNA in esa1 mutants. Although mutants of both ESA1 and SIR2 have enhanced rates of rDNA recombination, esa1 effects are more modest yet result in distinct structural changes of rDNA chromatin. Surprisingly, increased expression of ESA1 can bypass the requirement for Sir2p in rDNA silencing, suggesting that these two enzymes with seemingly opposing activities both contribute to achieve optimal nucleolar chromatin structure and function.

The online version of this article contains supplemental material at MBC Online (http://www.molbiolcell.org).

Present address: Whitehead Institute, Massachusetts Institute of Technology, 9 Cambridge Center, Cambridge, MA 02142

Present address: Gladstone Institute of Cardiovascular Disease, University of California, San Francisco, Room 430B, 1650 Owens Street, San Francisco, CA 94158.

Address correspondence to: Lorraine Pillus (lpillus{at}ucsd.edu).

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