Histone deacetylases govern heterochromatin in every phase

Abstract

Deacetylation of histone tails has been shown to play a role during heterochromatin formation, but the precise mechanism of action has not been understood. Complementary results presented in two recent articles in The EMBO Journal (Alper et al , 2013; Buscaino et al , 2013) together reveal how histone deacetylases (HDACs) affect the various phases of heterochromatin formation: establishment, maintenance and spreading. Heterochromatin, condensed chromatin that is transcriptionally inactive, plays important roles in epigenetic regulation of gene expression and other chromosomal functions, such as chromosome segregation and telomere maintenance. Fission yeast is a good model system to analyse heterochromatin because of the similarity of its heterochromatin structure to other eukaryotes and the ease of genetic analysis. In fact, this organism has contributed greatly to our understanding of the importance of RNA interference (RNAi) during heterochromatin formation. Heterochromatin is defined by methylation of lysine 9 of histone H3 (H3K9me) and hypo‐acetylation of histones. H3K9me provides the binding sites for heterochromatin protein 1, HP1 (Swi6 in fission yeast, Nakayama et al , 2001). Since deacetylation of histone tails by HDACs generally correlates with the repression of transcription at euchromatic regions, a similar function of HDACs is expected at heterochromatin. Indeed, the HDAC Clr3 is required for efficient repression of …