Originally published as Genetics Published Articles Ahead of Print on August 20, 2008.

Genetics, Vol. 180, 771-783, October 2008, Copyright © 2008
doi:10.1534/genetics.108.091710

The Ku Complex in Silencing the Cryptic Mating-Type Loci of Saccharomyces cerevisiae

* Laboratory of Genetics and {dagger} Department of Biomolecular Chemistry, University of Wisconsin School of Medicine and Public Health and College of Agricultural and Life Sciences, Madison, Wisconsin 53706

1 Corresponding author: Department of Biomolecular Chemistry, 587 MSC, 1300 University Ave., University of Wisconsin School of Medicine and Public Health, Madison, WI 53706-1532.
E-mail: cfox{at}wisc.edu

Sir1 establishes transcriptional silencing at the cryptic mating-type loci HMR and HML (HM loci) by recruiting the three other Sir proteins, Sir2, -3, and -4, that function directly in silenced chromatin. However, SIR1-independent mechanisms also contribute to recruiting the Sir2–4 proteins to the HM loci. A screen to elucidate SIR1-independent mechanisms that establish HMR silencing identified a mutation in YKU80. The role for Ku in silencing both HMR and HML was masked by SIR1. Ku's role in silencing the HM loci was distinct from its shared role with the nuclear architecture protein Esc1 in tethering the HM loci and telomeres to the nuclear periphery. The ability of high-copy SIR4 to rescue HMR silencing defects in sir1{Delta} cells required Ku, and chromatin immunoprecipitation (ChIP) experiments provided evidence that Ku contributed to Sir4's physical association with the HM loci in vivo. Additional ChIP experiments provided evidence that Ku functioned directly at the HM loci. Thus Ku and Sir1 had overlapping roles in silencing the HM loci.


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C. L. Vandre, R. T. Kamakaka, and D. H. Rivier
The DNA End-Binding Protein Ku Regulates Silencing at the Internal HML and HMR Loci in Saccharomyces cerevisiae
Genetics, November 1, 2008; 180(3): 1407 - 1418.
[Abstract] [Full Text] [PDF]