Originally published as Genetics Published Articles Ahead of Print on July 14, 2005.

Genetics, Vol. 171, 885-899, November 2005, Copyright © 2005
doi:10.1534/genetics.105.044719

Regulation of Histone Deposition Proteins Asf1/Hir1 by Multiple DNA Damage Checkpoint Kinases in Saccharomyces cerevisiae

Judith A. Sharp^*,1, Gizem Rizki^,2 and Paul D. Kaufman^,3

^* , Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, ^*,Department of Molecular and Cell Biology, University of California, Berkeley, California 94720 and Program in Gene Function and Expression, University of Massachusetts Medical School, Worcester, Massachusetts 01605

³ Corresponding author: Program in Gene Function and Expression, University of Massachusetts Medical School, 364 Plantation St., LRB506, Worcester, MA 01605.
E-mail: paul.kaufman1{at}umassmed.edu

CAF-1, Hir proteins, and Asf1 are histone H3/H4 binding proteins important for chromatin-mediated transcriptional silencing. We explored genetic and physical interactions between these proteins and S-phase/DNA damage checkpoint kinases in the budding yeast Saccharomyces cerevisiae. Although cells lacking checkpoint kinase Mec1 do not display defects in telomeric gene silencing, silencing was dramatically reduced in cells lacking both Mec1 and the Cac1 subunit of CAF-1. Silencing was restored in cac1 and cac1 mec1 cells upon deletion of Rad53, the kinase downstream of Mec1. Restoration of silencing to cac1 cells required both Hir1 and Asf1, suggesting that Mec1 counteracts functional sequestration of the Asf1/Hir1 complex by Rad53. Consistent with this idea, the degree of suppression of silencing defects by rad53 alleles correlated with effects on Asf1 binding. Furthermore, deletion of the Dun1 kinase, a downstream target of Rad53, also suppressed the silencing defects of cac1 cells and reduced the levels of Asf1 associated with Rad53 in vivo. Loss of Mec1 and Rad53 did not alter telomere lengths or Asf1 protein levels, nuclear localization, or chromosome association. We conclude that the Mec1 and Dun1 checkpoint kinases regulate the Asf1-Rad53 interaction and therefore affect the activity of the Asf1/Hir complex in vivo.

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