Orc4 spatiotemporally stabilizes centromeric chromatin

Abstract

Spatiotemporal regulation in DNA replication maintains kinetochore stability. The epigenetically regulated centromeres (CENs) in the budding yeast Candida albicans have unique DNA sequences, replicate early and are clustered throughout the cell cycle. In this study, the genome-wide occupancy of replication initiation protein Orc4 reveals its abundance at all CENs in C. albicans. Orc4 associates with four different DNA motifs, one of which coincides with tRNA genes. Hi-C combined with genome-wide replication timing analyses identify enriched interactions among early or late replicating Orc4-bound regions. A simulated polymer model of chromosomes reveals that early replicating and strongly enriched Orc4-bound sites localize towards the kinetochores. Orc4 is constitutively localized to CENs, and both Orc4 and Mcm2 stabilize CENPA. CENPA chaperone Scm3 localizes at the kinetochore during anaphase, coinciding with the loading time of CENPA. We propose that this spatiotemporal nuclear localization of Orc4, with Mcm2 and Scm3, recruits CENPA and stabilizes centromeric chromatin.