Pivotal roles of PCNA loading and unloading in heterochromatin function.

In , heterochromatin structures required for transcriptional silencing of the and loci are duplicated in coordination with passing DNA replication forks. Despite major reorganization of chromatin structure, the heterochromatic, transcriptionally silent states of and are successfully maintained throughout S-phase. Mutations of specific components of the replisome diminish the capacity to maintain silencing of and through replication. Similarly, mutations in histone chaperones involved in replication-coupled nucleosome assembly reduce gene silencing. Bridging these observations, we determined that the proliferating cell nuclear antigen (PCNA) unloading activity of Elg1 was important for coordinating DNA replication forks with the process of replication-coupled nucleosome assembly to maintain silencing of and through S-phase. Collectively, these data identified a mechanism by which chromatin reassembly is coordinated with DNA replication to maintain silencing through S-phase.