title: ASH1, a Drosophila trithorax group protein, is required for methylation of lysine 4 residues on histone H3.
abstract: Covalent modifications of histone tails modulate gene expression via chromatin organization. As examples, methylation of lysine 9 residues of histone H3 (H3) (H3-K9) is believed to repress transcription by compacting chromatin, whereas methylation of lysine 4 residues of H3 (H3-K4) is believed to activate transcription by relaxing chromatin. The Drosophila trithorax group protein absent, small, or homeotic discs 1 (ASH1) is involved in maintaining active transcription of many genes. Here we report that in extreme ash1 mutants, no H3-K4 methylation is detectable. Within the limits of our assays, this lack of detectable H3-K4 methylation implies that ASH1 is required for essentially all H3-K4 methylation that occurs in vivo. We report further that the 149-aa SET domain of ASH1 is sufficient for H3-K4 methylation in vitro. These findings support a model in which ASH1 is directly involved in maintaining active transcription by conferring a relaxed chromatin structure.
mesh_terms: D000818:Animals; D004268:DNA-Binding Proteins; D004330:Drosophila; D029721:Drosophila Proteins; D005455:Fluorescent Antibody Technique; D006657:Histones / Q000378:metabolism*; D008239:Lysine / Q000378:metabolism*; D008745:Methylation; D009154:Mutation; D014157:Transcription Factors / Q000502:physiology*
chemical_list: C490910:ASH1 protein, Drosophila; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D006657:Histones; D014157:Transcription Factors; D008239:Lysine