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Eukaryotic Cell, November 2006, p. 1925-1933, Vol. 5, No. 11
1535-9778/06/$08.00+0     doi:10.1128/EC.00105-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Effect of Sequence-Directed Nucleosome Disruption on Cell-Type-Specific Repression by 2/Mcm1 in the Yeast Genome

Nobuyuki Morohashi,¹ Yuichi Yamamoto,¹ Shunsuke Kuwana,¹ Wataru Morita,¹ Heisaburo Shindo,² Aaron P. Mitchell,³ and Mitsuhiro Shimizu^1*

Department of Chemistry, Meisei University, Hino, Tokyo 191-8506, Japan,¹ School of Pharmacy, Tokyo University of Pharmacy and Life Science, Hachioji, Tokyo 192-0392, Japan,² Department of Microbiology, Columbia University, New York, New York 10032³

Received 12 April 2006/ Accepted 31 August 2006

In Saccharomyces cerevisiae, a-cell-specific genes are repressed in MAT cells by 2/Mcm1, acting in concert with the Ssn6-Tup1 corepressors and the Isw2 chromatin remodeling complex, and nucleosome positioning has been proposed as one mechanism of repression. However, prior studies showed that nucleosome positioning is not essential for repression by 2/Mcm1 in artificial reporter plasmids, and the importance of the nucleosome positioning remains questionable. We have tested the function of positioned nucleosomes through alteration of genomic chromatin at the a-cell-specific gene BAR1. We report here that a positioned nucleosome in the BAR1 promoter is disrupted in cis by the insertion of diverse DNA sequences such as poly(dA) · poly(dT) and poly(dC-dG) · poly(dC-dG), leading to inappropriate partial derepression of BAR1. Also, we show that isw2 mutation causes loss of nucleosome positioning in BAR1 in MAT cells as well as partial disruption of repression. Thus, nucleosome positioning is required for full repression, but loss of nucleosome positioning is not sufficient to relieve repression completely. Even though disruption of nucleosome positioning by the cis- and trans-acting modulators of chromatin has a modest effect on the level of transcription, it causes significant degradation of the -mating pheromone in MAT cells, thereby affecting its cell type identity. Our results illustrate a useful paradigm for analysis of chromatin structural effects at genomic loci.

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* Corresponding author. Mailing address: Department of Chemistry, Meisei University, 2-1-1 Hodokubo, Hino, Tokyo 191-8506, Japan. Phone: 81-42-591-7483. Fax: 81-42-591-8181. E-mail: shimizum{at}chem.meisei-u.ac.jp.

Published ahead of print on 15 September 2006.

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Eukaryotic Cell, November 2006, p. 1925-1933, Vol. 5, No. 11
1535-9778/06/$08.00+0     doi:10.1128/EC.00105-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

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