Histone H3 globular domain acetylation identifies a new class of enhancers

Wendy Bickmore, Madapura Pradeepa and colleagues identify a new class of active enhancers marked by histones with modifications on residues in the globular domain. They find that H3K64ac and H3K122ac are markers for active promoters and enhancers in embryonic stem cells and human cancer cell lines. Histone acetylation is generally associated with active chromatin, but most studies have focused on the acetylation of histone tails. Various histone H3 and H4 tail acetylations mark the promoters of active genes1. These modifications include acetylation of histone H3 at lysine 27 (H3K27ac), which blocks Polycomb-mediated trimethylation of H3K27 (H3K27me3)2. H3K27ac is also widely used to identify active enhancers3,4, and the assumption has been that profiling H3K27ac is a comprehensive way of cataloguing the set of active enhancers in mammalian cell types. Here we show that acetylation of lysine residues in the globular domain of histone H3 (lysine 64 (H3K64ac) and lysine 122 (H3K122ac)) marks active gene promoters and also a subset of active enhancers. Moreover, we find a new class of active functional enhancers that is marked by H3K122ac but lacks H3K27ac. This work suggests that, to identify enhancers, a more comprehensive analysis of histone acetylation is required than has previously been considered.