Analysis of the Histone H3.1 Interactome: A Suitable Chaperone for the Right Event

Despite minimal disparity at the sequence level, mammalian H3 variants bind to distinct sets of polypeptides. Although histone H3.1 predominates in cycling cells, our knowledge of the soluble complexes that it forms en route to deposition or following eviction from chromatin remains limited. Here, we provide a comprehensive analysis of the H3.1-binding proteome, with emphasis on its interactions with histone chaperones and components of the replication fork. Quantitative mass spectrometry revealed 170 protein interactions, whereas a large-scale biochemical fractionation of H3.1 and associated enzymatic activities uncovered over twenty stable protein complexes in dividing human cells. The sNASP and ASF1 chaperones play pivotal roles in the processing of soluble histones but do not associate with the active CDC45/MCM2–7/GINS (CMG) replicative helicase. We also find TONSL-MMS22L to function as a H3-H4 histone chaperone. It associates with the regulatory MCM5 subunit of the replicative helicase. [Display omitted] •Human H3.1 stably interacts with eleven histone chaperones in HeLa cells•TONSL-MMS22L functions as a histone chaperone•TONSL binds MCM5 Campos et al. use quantitative mass spectrometry to identify 170 H3.1-interactions corresponding to over twenty protein complexes. The complexes were examined for intrinsic enzymatic activities, including nucleosomal histone eviction activity. TONSL was found to act as an H3.1 histone chaperone. TONSL binds MCM5 and methylated histones.