Physical and functional association of SU(VAR)3-9 and HDAC1 in Drosophila

Modification of histones can have a dramatic impact on chromatin structure and function. Acetylation of lysines within the N-terminal tail of the hist one octamer marks transcriptionally active regions of the genome whereas de acetylation seems to play a role in transcriptional silencing. Recently, th e methylation of the histone tails has also been shown to be important for transcriptional regulation and chromosome structure. Here we show by immuno affinity purification that two activities important for chromatin-mediated gene silencing, the histone methyltransferase SU(VAR)3-9 and the histone de acetylase HDAC1, associate in vivo. The two activities cooperate to methyla te pre-acetylated histones. Both enzymes are modifiers of position effect v ariegation and interact genetically in flies. We suggest a model in which t he concerted histone deacetylation and methylation by a SU(VAR)3-9/HDAC1-co ntaining complex leads to a permanent silencing of transcription in particu lar areas of the genome.