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Molecular and Cellular Biology, March 2007, p. 1925-1933, Vol. 27, No. 5
0270-7306/07/$08.00+0 doi:10.1128/MCB.01619-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Department of Biology, University of Rochester, Rochester, New York 14627
Received 30 August 2006/ Returned for modification 24 October 2006/ Accepted 12 December 2006
Tetrahymena thermophila macronuclear histone H1 is phosphorylated by a cdc2 kinase, and H1 phosphorylation regulates CDC2 expression by a positive feedback mechanism. In starved wild-type cells, decreased expression of the CDC2 gene is correlated with a global reduction in the phosphorylation of H1 and reduced phosphorylation of H1 in the region upstream of the CDC2 gene. To determine whether the reduced H1 phosphorylation upstream of the CDC2 gene is merely a reflection of global dephosphorylation or is due to specific targeting of dephosphorylation of H1 to the CDC2 promoter during starvation, the CDC2 promoter was mapped, and the distributions of phosphorylated and unphosphorylated H1 across the CDC2 gene were determined using chromatin immunoprecipitation. Unphosphorylated H1 is specifically enriched in a region of the CDC2 promoter when the gene's expression is reduced during starvation but not when CDC2 is highly active in growing cells. The region of unphosphorylated H1 coincides with a region that is essential for CDC2 expression. These studies are the first in vivo demonstration that the phosphorylation of H1 is being regulated at a fine level and that unphosphorylated H1 can be specifically targeted to a promoter, where it likely regulates transcription in a gene-specific manner.
Published ahead of print on 28 December 2006.
Present address: School of Medicine, UCSD, La Jolla, CA 92037.
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