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Eukaryotic Cell doi:10.1128/EC.00217-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

The class I HDAC Thd1p promotes global chromatin condensation in Tetrahymena thermophila

Joint Science Department, W. M. Keck Science Center, Claremont Colleges, Claremont, California 91711; Department of Biology, Mount Holyoke College, South Hadley, Massachussetts 01075

^* To whom correspondence should be addressed. Email: ewiley{at}jsd.claremont.edu.

	Abstract

Class I histone deacetylases (HDACs) regulate DNA-templated processes such as transcription. They act both at specific loci and more generally across global chromatin, contributing to acetylation patterns that may underlie large-scale chromatin dynamics. Although hypoacetylation is correlated with highly condensed chromatin, little is known about the contribution of individual HDACs to chromatin condensation mechanisms. Using the ciliated protozoan Tetrahymena thermophila we investigated the role of a specific class I HDAC, Thd1p, in reversible condensation of global chromatin. In this system, the normal physiological response to cell starvation includes widespread condensation of macronuclear chromatin and general repression of gene transcription. We show that chromatin in Thd1p-deficient cells failed to condense during starvation. Condensation failure correlated with aberrant hyperphosphorylation of histone H1 and overexpression of CDC2 encoding the major histone H1 kinase. Changes in the rate of acetate turnover on core histones and in the distribution of acetylated lysines 9 and 23/27 on histone H3 isoforms, that were found to correlate with normal chromatin condensation, were absent from Thd1p mutant cells. These results point to a role for a class I HDAC in the formation of reversible higher order chromatin structures and global genome compaction through mechanisms involving the regulation of H1 phosphorylation and core histone acetylation/deacetylation kinetics.

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