The Mcm2-Ctf4-Pola axis facilitates parental histone transfer to lagging strands

Although essential for epigenetic inheritance, the transfer of parental histone (H3-H4)2 tetramers that contain epigenetic modifications to replicating DNA strands is poorly understood. Here, we show that the Mcm2-Ctf4-Pol axis facilitates the transfer of parental (H3-H4)2 tetramers to lagging strands of DNA replication forks. Mutating the H3-H4 binding domain of Mcm2, a subunit of the CMG (Cdc45-MCM-GINS) replicative helicase that translocates along leading strands, impairs the transfer of parental (H3-H4)2 to lagging strands. Similar effects are observed in Ctf4 and Pol-primase mutants that disrupt the connection of the CMG helicase via Ctf4-Pol to lagging strands. Our results support a model whereby parental (H3-H4)2 displaced from nucleosomes through leading-strand DNA replication are transferred to lagging strands for nucleosome assembly via the CMG-Ctf4-Pol complex. We synchronized yeast cells (Wild type and other mutant cells) at G1 and released into early S phase in the presence of BrdU, and with or without hydroxyurea (HU). We then performed BrdU immunoprecipitation using anti-BrdU antibodies following single-strand DNA library preparation and sequencing (ssSeq). we also performed protein ChIP followed by single-strand DNA sequencing (ChIP-ssSeq) for Ctf4, H3K56ac, H3K4me3, T7-tag, and HA-tag. Also eSPAN for Ctf4, H3K56ac, H3K4me3, T7-tag, and HA-tag. The sequencing tag was mapped to both Watson (red) and Crick (blue) strands of the reference genome.