Identification of H3 Lysine 4 monomethylation Associated Proteins at Mammalian Enhancers

Enhancers act to regulate cell type specific gene expression by facilitating the transcription of target genes. In mammalian cells active or primed enhancers are commonly marked by mono-methylation of Histone H3 at lysine 4 (H3K4me1) in a cell-type specific manner. While this histone modification regulates enhancer-dependent transcription programs in mammals, the exact mechanism has remained unclear. In the current study, we conducted SILAC Mass-spec experiments with mono-nucleosomes and identified multiple H3K4me1 associated proteins, including the mediator complex, Cohesin complex, as well as proteins involved in chromatin remodeling. We demonstrate that binding of these protein complexes to enhancers in vivo depends on H3K4me1. We have characterized the PHD domains of DPF1-3 and PHF10 and identified the amino acids involved in binding to H3K4me1. In addition, we discovered that H3K4me1 nucleosomes are more efficiently remodeled by BAF complex in vitro. Our results suggest that H3K4me1 plays an active role at enhancers through binding of a diverse set of chromatin regulators. Examination of colocalization of multiple chromatin regulator complexes with H3K4me1 and dependency on H3K4me1 at mouse enahncers.