Biochemical characterization of H3K4 methyltransferase complexes

Abstract

Methylation on lysine 4 of histone H3 (H3K4) is one of the prominent histone modification marks that correlate strongly with active transcription in eukaryotes. Accumulating studies in metazoans have implicated misregulation of H3K4 methylation in the pathogenesis of cancer and in developmental defects, further emphasizing the importance of understanding the regulation of H3K4 methylation. Presence of at least six H3K4 methyltransferase (SET1A, SET1B, MLL1, MLL2, MLL3 and MLL4) complexes has complicated functional characterization of each complex because of their possible redundant and non-redundant roles. To understand roles of H3K4 methyltransferases in transcriptional regulation in eukaryotic cells, we have deployed histone methyltransferase assays, subunit interaction studies and transcription assays using purified human H3K4 methyltransferase complexes. Our studies establish minimal components of the H3K4 methyltransferase complexes required for H3K4 methylation and provide a mechanistic basis for H3K4 methylation in mammalian cells.