Abstract
All vertebrate genomes encode for three large histone H2A variants that have an additional metabolite-binding globular macrodomain module, macroH2A. MacroH2A variants impact heterochromatin organization and transcription regulation and establish a barrier for cellular reprogramming. However, the mechanisms of how macroH2A is incorporated into chromatin and the identity of any chaperones required for histone deposition remain elusive. Here, we develop a split-GFP-based assay for chromatin incorporation and use it to conduct a genome-wide mutagenesis screen in haploid human cells to identify proteins that regulate macroH2A dynamics. We show that the histone chaperone ANP32B is a regulator of macroH2A deposition. ANP32B associates with macroH2A in cells and invitro binds to histones with low nanomolar affinity. Invitro nucleosome assembly assays show that ANP32B stimulates deposition of macroH2A-H2B and not of H2A-H2B onto tetrasomes. In cells, depletion of ANP32B strongly affects global macroH2A chromatin incorporation, revealing ANP32B as a macroH2A histone chaperone.
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