Rif1 regulates the replication timing domains on the human genome

DNA replication is spatially and temporally regulated during S-phase. DNA replication timing is established in early G1-phase at a point referred to as TDP (timing decision point). We show that Rif1 (Rap1-interacting-factor1), originally identified as a telomere binding factor in yeast, is a critical determinant of the replication timing program in human cells. Depletion of Rif1 results in specific loss of mid-S replication foci profiles, stimulation of initiation events in early S-phase and changes in long-range replication timing domain structures. Overall replication timing is shifted toward mid-S in both directions, suggesting that replication timing regulation is abrogated in the absence of Rif1. Rif1 tightly binds to nuclear insoluble structures at late-M to early-G1 and regulates the chromatin-loop sizes. Furthermore, Rif1 colocalizes specifically with the mid-S replication foci. Thus, Rif1 establishes the mid-S replication domains that are restrained from being activated at early S-phase. Our results indicate that Rif1 plays crucial roles in determining the replication timing domain structures through regulating higher-order chromatin architecture. HeLa cells (ATCC), with a total of 4 individual replicates