Collective regulation of chromatin modifications predicts replication timing during cell cycle.

Replication timing (RT) associates with genome architecture, while having a mixed relationship to histone marks. By profiling replication at high resolution and assessing broad histone marks across the cell cycle at the resolution of RT with and without genetic perturbation, we address the causal relationship between histone marks and RT. Four primary chromatin states, including an uncharacterized H3K36me2 state, emerge and define 97% of the mappable genome. RT and local replication patterns (e.g., initiation zones) quantitatively associate with chromatin states, histone mark dynamics, and spatial chromatin structure. Manipulation of broad histone marks and enhancer elements by overexpressing the histone H3 lysine 9/36 tri-demethylase KDM4A impacts RT across 11% of the genome. Broad histone modification changes were strong predictors of the observed RT alterations. Lastly, replication within H3K36me2-enriched neighborhoods is sensitive to KDM4A overexpression and is controlled at a megabase scale. These studies establish a role for collective chromatin mark regulation in modulating RT.