Biochemical characterization of the human H3K4 methyltransferase complexes

Abstract

Nuclear DNA in eukaryotic cells is organized within a hierarchical chromatin structure that restricts access to regulatory enzymes. Especially, the protruding histone tails are susceptible to posttranslational modifications. Above all, histone H3 lysine 4 (H3K4) methylation is one of the prominent histone modification marks that correlates strongly with active transcription. Mammalian cells have at least six H3K4 HMTases, thus implicating their possible redundant and unique roles. For biochemical characterization of the human H3K4 HMTase complexes, we reconstituted and purified three full-length and six core complexes following to be subjected in an in vitro histone methyltransferase assay, all complexes exhibit differential H3K4 HMTase activity toward recombinant chromatins, indicating all have intrinsic H3K4 HMTase activity. We also found that both SET1A/B complex has the strongest histone H2B ubiquitylation-dependent H3K4 HMTase activity. These data suggest that human H3K4 HMTase complexes have distinctive mechanism of action during H3K4 methylation. More detailed biochemical analyses will help us to understand functions and molecular mechanisms of H3K4 methylation in human.