We have conducted a genomewide investigation into the enzymatic specificity, expression profiles, and binding locations of four histone deacetylases (HDACs), representing the three different phylogenetic classes in fission yeast ( Schizosaccharomyces pombe). By directly comparing nucleosome density, histone acetylation patterns and HDAC binding in both intergenic and coding regions with gene expression profiles, we found that Sir2 ( class III) and Hos2 ( class I) have a role in preventing histone loss; Clr6 ( class I) is the principal enzyme in promoter-localized repression. Hos2 has an unexpected role in promoting high expression of growth-related genes by deacetylating H4K16Ac in their open reading frames. Clr3 ( class II) acts cooperatively with Sir2 throughout the genome, including the silent regions: rDNA, centromeres, mat2/3 and telomeres. The most significant acetylation sites are H3K14Ac for Clr3 and H3K9Ac for Sir2 at their genomic targets. Clr3 also affects subtelomeric regions which contain clustered stress- and meiosis-induced genes. Thus, this combined genomic approach has uncovered different roles for fission yeast HDACs at the silent regions in repression and activation of gene expression.

Expression profiling, ChiP-CHIP and phenotypic analysis were used to investigate the functional relationships of class III NAD(+)-dependent HDACs (Sirtuins) in fission yeast. We detected significant histone acetylation increases in Sirtuin mutants at their specific genomic binding targets and were thus able to identify an in vivo substrate preference for each Sirtuin. At heterochromatic loci, we demonstrate that although Hst2 is mainly cytoplasmic, a nuclear pool of Hst2 colocalizes with the other Sirtuins at silent regions (cen, mat, tel, rDNA), and that like the other Sirtuins, Hst2 is required for rDNA and centromeric silencing. Interestingly we found specific functions for the fission yeast Sirtuins Hst2 and Hst4 in gene regulation. Hst2 directly represses genes involved in transport and membrane function, whereas Hst4 represses amino-acid biosynthesis genes and Tf2 retrotransposons. A specific role for Hst4 in Tf2 50 mRNA processing was revealed. Thus, Sirtuins share functions at many genomic targets, but Hst2 and Hst4 have also evolved unique functions in gene regulation.

We have used oligonucleotide tiling arrays to construct genome-wide high-resolution histone acetylation maps for fission yeast. The maps are corrected for nucleosome density and reveal surprisingly uniform patterns of modifications for five different histone acetylation sites. We found that histone acetylation and methylation patterns are generally polar, i.e. they change as a function of distance from the ATG codon. A typical fission yeast gene shows a distinct peak of histone acetylation around the ATG and gradually decreased acetylation levels in the coding region. The patterns are independent of gene length but dependent on the gene expression levels. H3K9Ac shows a stronger peak near the ATG and is more reduced in the coding regions of genes with high expression compared with genes with low expression levels. H4K16Ac is strongly reduced in coding regions of highly expressed genes. A second microarray platform was used to confirm the 5' to 3' polarity effects observed with tiling microarrays. By comparing coding region histone acetylation data in HDAC mutants and wild type, we found that hos2 affects primarily the 5' regions, sir2 and clr6 affect middle regions, and clr6 affects 3' regions. Thus, mechanisms involving different HDACs modulate histone acetylation levels to maintain a 5' to 3' polarity within the coding regions.

To map histone modifications with unprecedented resolution both globally and locus-specifically, and to link modification patterns to gene expression. Materials & methods: Using correlations between quantitative mass spectrometry and chromatin immunoprecipitation/microarray analyses, we have mapped histone post-translational modifications in fission yeast (Schizosaccharomyces pombe). Results: Acetylations at lysine 9, 18 and 27 of histone H3 give the best positive correlations with gene expression in this organism. Using clustering analysis and gene ontology search tools, we identified promoter histone modification patterns that characterize several classes of gene function. For example, gene promoters of genes involved in cytokinesis have high H3K36me2 and low H3K4me2, whereas the converse pattern is found ar promoters of gene involved in positive regulation of the cell cycle. We detected acetylation of H4 preferentially at lysine 16 followed by lysine 12, 8 and 5. Our analysis shows that this H4 acetylation bias in the coding regions is dependent upon gene length and linked to gene expression. Our analysis also reveals a role for H3K36 methylation at gene promoters where it functions in a crosstalk between the histone methyltransferase Set2(KMT3) and the histone deacetylase Clr6, which removes H3K27ac leading to repression of transcription. Conclusion: Histone modification patterns could be linked to gene expression in fission yeast.