Chromatin Replication, Epigenetic Inheritance, and Beyond

Chromatin replication is one of the most sophisticated molecular processes within cells, wielding profound influence over epigenetic inheritance and genome integrity. It involves a series of intricate steps, from the disassembly of parental nucleosomes and unwinding of the double-stranded DNA (dsDNA) to the synthesis of daughter strands, followed by the reassembly of nucleosomes onto these newly formed daughter strands. This process occurs in a stepwise manner and demands tight coordination between each stage. Two major sets of protein machineries, the DNA replication machinery (Replisome) and the nucleosome assembly machinery (histone chaperones and remodelers), must “effectively communicate” to ensure that the entire process proceeds smoothly and in a highly coordinated manner.

In this presentation, I will discuss our current understanding of the coordination mechanisms between histone chaperones and replisome components. First, I will present our recent progress in elucidating the role of the histone chaperone FACT (Facilitates Chromatin Transactions) in collaborating with replisome components to manage the recycling and distribution of parental histones at replication forks. We discovered that FACT anchors to the replisome via its Spt16-N terminus, facilitating the transfer of parental histones to both the leading and lagging strands. Furthermore, FACT collaborates with the Fork Protection Complex (FPC), composed of Tof1, Csm3, and Mrc1, to regulate the recycling and distribution of parental histones between the two daughter strands. Additionally, I will highlight how various histone chaperones interact with RPA and DNA polymerases to regulate histone trafficking and facilitate strand-specific nucleosome assembly. We propose that this efficient collaboration between histone chaperones and the replisome is crucial for maintaining the efficiency, balance, and symmetry of histone trafficking during chromatin replication, which ultimately supports the inheritance of epigenetic information. Second, I will present our recent findings on the coordination mechanism between FACT and DNA polymerase a. We discovered that the histone H3-H4, but not H2A-H2B, mediates the interaction between FACT and Pol α. This interaction stimulates Pol α’s activity and is crucial for Okazaki fragment synthesis and replication fork progression. We propose that the FACT-(H3-H4)-Pol α interaction acts as a “Pre-Warning System”, regulating DNA replication to ensure proper coordination between DNA synthesis and nucleosome assembly, thereby safeguarding genome integrity.