Characterization of Arabidopsis homologs of the Drosophila SET domain gene Su(var)3-9

Abstract

SET domain-containing proteins encoded by the Drosophila gene Su(var)3-9 and its human homologue, SUV39H1, are major regulators of heterochromatin formation. The SET domains of these proteins carry histone methyltransferase activity, which specifically targets lysine 9 of histone H3. Thus far, although nineteen Su(var)3-9 homologs (SUVH genes) have been identified in plants on the basis of SET domain similarities, few have been characterized in detail. The work described herein began with an investigation of the phylogenetic relationships of plant SUVH genes all of which share a similar domain architecture, comprising a SET domain flanked by pre-SET and post-SET domains and a novel domain named SRA. Analysis of selective constraints in the SRA and SET domains during SUVH evolution indicates that after gene duplication, functional divergence of the SRA domain occurred in different SUVH lineages. The SET domain by contrast has remained under strong purifying selection.