title: Identification of three histone methyltransferases in Drosophila: dG9a is a suppressor of PEV and is required for gene silencing.
abstract: Organization of chromatin structure and regulation of gene transcription are contingent on histone tail modifications. Regions of the genome packaged with nucleosomes that contain methyl histone H3 at lysine 9 (Me K9H3) strongly correlate with regions that are silenced for transcription. To date Su(var)3-9 is the only K9H3 specific enzyme characterized in Drosophila melanogaster. In this study, we describe the identification of three additional Drosophila genes that potentially encode K9H3 specific methyltransferases (HMTase) with homology to known mammalian proteins. By several criteria, including sequence alignments, phylogenic analyses, and enzyme activity of the protein, one of these is a homologue of the human G9a and hence, we name it dG9a. dG9a catalyzes the transfer of methyl groups to full-length histone H3 and to N-terminal H3 peptides that contain lysine 9, suggesting that the major target for dG9a is K9H3. Chromatin extracts prepared from a P-element insert mutation in dG9a display an altered K9H3 methylation profile. In addition, the dG9a mutant is a dominant suppressor of position-effect variegation (PEV), a heterochromatin-associated gene silencing phenomenon. Su(var)3-9 also suppresses PEV. The combined Su(var)3-9 and dG9a mutations have severe developmental defects suggesting an overlapping role for dG9a and Su(var)3-9 in the packaging of heterochromatin and gene silencing via a K9H3 methylation pathway.
authors.affiliation: Department of Zoology, Life Sciences Institute, University of British Columbia, 2350 Health Sciences Mall, Vancouver, BC, Canada, V6T 1Z3.
authors.forename: Jacek
authors.initials: J
authors.lastname: Mis
authors.forename: Sarbjit S
authors.initials: SS
authors.lastname: Ner
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Grigliatti
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015153:Blotting, Western; D017931:DNA Primers; D004331:Drosophila melanogaster / Q000201:enzymology*; D020868:Gene Silencing; D000076983:Histone Methyltransferases; D011495:Histone-Lysine N-Methyltransferase / Q000737:chemistry / Q000235:genetics*; D006801:Humans; D008969:Molecular Sequence Data; D011496:Protein Methyltransferases; D017386:Sequence Homology, Amino Acid
chemical_list: D017931:DNA Primers; D000076983:Histone Methyltransferases; D011496:Protein Methyltransferases; D011495:Histone-Lysine N-Methyltransferase