While DNA replication has been extensively studied biochemically and even the entire replication initiation process of budding yeast has been reconstituted in vitro. However, the chromatin accommodates multiple DNA metabolism events and has its hierarchic structures. There, thousands of replication forks need to navigate in complex chromatin environments, avoiding collision with other DNA metabolism activities, and finally fulfill faithful duplication of genome and epigenetic modifications. In this context, the organization of multiple DNA replication forks in mammalian cells and the influence of chromatin structures on DNA replication remain poorly understood
