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Mechanisms of enhanced silencing in rpd3 delete strains of Saccharomyces cerevisiae
Author(s) -
Kleinschmidt Richard Alton,
Donze David
Publication year - 2009
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.23.1_supplement.lb189
Subject(s) - biology , heterochromatin , genetics , gene silencing , saccharomyces cerevisiae , heterochromatin protein 1 , chromatin , histone , dna methylation , histone deacetylase , gene , gene expression
In Saccharomyces cerevisiae , heterochromatic silencing occurs at the cryptic‐mating loci HMRa and HMLα , ribosomal DNA, and telomeres. Propagation of silent heterochromatin is sequence‐independent mediated by the Silent Information Regulator proteins (e.g. Sir3p) and other factors involved in repression. Rpd3p is part of a larger histone deacetylase complex that represses transcription when targeted by promoter‐specific transcription factors. In yeast, RPD3 deletion surprisingly enhances silencing at the cryptic mating loci and telomeres (Vannier et al. 1996), even overriding the tDNA barrier element adjacent to the HMR locus (Donze and Kamakaka, 2001, Jambunathan et al 2005). To understand the mechanism of enhanced silencing in strains lacking RPD3 , we mutagenized rpd3 D strains containing an ADE2 marker gene adjacent to HMR and identified suppressor mutants no longer displaying enhanced silencing. We identified seven genes which may affect heterochromatin formation in rpd3Δ backgrounds: BRE1, GDH2, BRE2, GAT3, QNS1, NPT1 and RXT3 . After deleting each of these genes in the rpd3Δ background, only BRE1 or BRE2 deleted strains crossed with rpd3Δ strains showed a loss of extended silencing at the HMR and a marked telomere. BRE1 and BRE2 are indirectly and directly involved in the tri‐methylation of histone H3 lysine 4 respectively. Other studies of histone H3 lysine 4 methylation have suggested that mutations in this pathway lead to a re‐distribution of Sir proteins at silenced loci (Madhani et al. 2007). We hypothesize that the increased silencing in rpd3 D mutants might also be due to redistribution of chromatin proteins. Future experiments will utilize ChIP‐Seq and DamID methodologies to determine Sir3p occupancy at HMR and genome‐wide euchromatic regions in WT vs. rpd3Δ strains. Support for this project was provided by a grant from the National Science Foundation.