Abstract

Chromatin plasticity and epigenetic memory, fundamental for eukaryotic biology, are determined by differential/regulated de novo deposition or recycling of pre-existing histones, which in turn dictate transcriptional programs. Recruitment of the histone-H3 variant, H3.3, mediated by the HIRA chaperone complex, is both causally and consequentially associated with transcription. Despite decades of work, endogenous regulatory mechanisms that differentiate between de novo deposition and recycling activities of HIRA are still unknown. Here, we have investigated the pivotal role of HIRA de-/acetylation in regulating its function. Our results unequivocally establish function separation effects of acetyl and deacetyl mimic mutations of lysine-600, vis-a-vis de novo deposition or recycling of H3.3, respectively. Importantly, we demonstrate that HIRA deacetylation-dependent biased H3.3 recycling determines transcriptional output, possibly through preferential enrichment of H3.3-K36me3. Besides unraveling tunable regulatory mechanism that governs HIRA function, we illustrate a causal link between the chaperone activity, biased recruitment of pre-existing histones, and gene expression.