BAHCC1 binds H4K20me1 to facilitate the MCM complex loading and DNA replication

Mono-methylation of histone H4 lysine 20 (H4K20me1) is increasingly appreciated to be critical for regulating genomic DNA replication, cell cycle progression and DNA damage repair. How exactly H4K20me1 regulates these biological processes remains murky. Here, we report that an evolutionarily conserved tandem Tudor domain (TTD) in the BAH Domain And Coiled-Coil Containing 1 (BAHCC1) protein (BAHCC1_TTD) selectively reads H4K20me1 for facilitating the replication origin activation and efficient DNA replication. Our integrated biochemical, structural, genomic and cellular analyses demonstrated that BAHCC1_TTD preferentially recognizes H4K20me1 to promote the recruitment of BAHCC1 and its interacting partners, notably the Mini-chromosome Maintenance (MCM) complex, to the replication origin sites. Combined actions of the H4K20me1-reading BAHCC1 and the H4K20me2-reading Origin Recognition Complex (ORC) ensure optimal genomic loading of MCM complexes for facilitating DNA replication. Depletion of BAHCC1, or disruption of the BAHCC1_TTD:H4K20me1 interaction, reduces levels of H4K20me1 and MCM loading, leading to defects in replication and cell cycle progression. Together, this study identifies BAHCC1_TTD as a conserved effector transducing the H4K20me1 signals to the recruitment of MCM complexes for facilitating efficient DNA replication.