H3K9me-independent gene silencing in fission yeast heterochromatin by Clr5 and histone deacetylases

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Klavs R Hansen, Idit Hazan, Sreenath Shanker, Stephen Watt, Janne Verhein Hansen, Jürg Bähler, Robert A Martienssen, Janet F Partridge, Amikam Cohen, Genevieve Thon

Nucleosomes in heterochromatic regions bear histone modifications that distinguish them from euchromatic nucleosomes. Among those, histone H3 lysine 9 methylation (H3K9me) and hypoacetylation have been evolutionarily conserved and are found in both multicellular eukaryotes and single-cell model organisms such as fission yeast. In spite of numerous studies, the relative contributions of the various heterochromatic histone marks to the properties of heterochromatin remain largely undefined. Here, we report that silencing of the fission yeast mating-type cassettes, which are located in a well-characterized heterochromatic region, is hardly affected in cells lacking the H3K9 methyltransferase Clr4. We document the existence of a pathway parallel to H3K9me ensuring gene repression in the absence of Clr4 and identify a silencing factor central to this pathway, Clr5. We find that Clr5 controls gene expression at multiple chromosomal locations in addition to affecting the mating-type region. The histone deacetylase Clr6 acts in the same pathway as Clr5, at least for its effects in the mating-type region, and on a subset of other targets, notably a region recently found to be prone to neo-centromere formation. The genomic targets of Clr5 also include Ste11, a master regulator of sexual differentiation. Hence Clr5, like the multi-functional Atf1 transcription factor which also modulates chromatin structure in the mating-type region, controls sexual differentiation and genome integrity at several levels. Globally, our results point to histone deacetylases as prominent repressors of gene expression in fission yeast heterochromatin. These deacetylases can act in concert with, or independently of, the widely studied H3K9me mark to influence gene silencing at heterochromatic loci.
Original languageEnglish
JournalP L o S Genetics
Issue number1
Number of pages16
Publication statusPublished - 2011

    Research areas

  • Amino Acid Sequence, Chromosomal Proteins, Non-Histone, Gene Expression Regulation, Fungal, Gene Silencing, Heterochromatin, Histone Deacetylases, Histone-Lysine N-Methyltransferase, Histones, Methylation, Molecular Sequence Data, Mutation, Schizosaccharomyces, Schizosaccharomyces pombe Proteins, Sequence Alignment, Sequence Homology, Amino Acid, Transcription Factors

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