Abstract：
Eukaryotic DNA replication is a tightly controlled process that occurs in two main steps, i.e., licensing and firing, which take place in the G1 and S phases of the cell cycle, respectively. In Saccharomyces cerevisiae, the budding yeast, replication origins contain consensus sequences that are recognized and bound by the licensing factor Orc1-6, which then recruits the replicative Mcm2-7 helicase. By contrast, mammalian initiation sites lack such consensus sequences, and the mammalian ORC does not exhibit sequence specificity. Studies performed over the past decades have identified replication initiation sites in the mammalian genome using sequencing-based assays, raising the question of whether replication initiation occurs at confined sites or in broad zones across the genome. Although recent reports have shown that the licensed MCMs in mammalian cells are broadly distributed, suggesting that ORC-dependent licensing may not determine the initiation sites/zones, they are predominantly located upstream of actively transcribed genes. This review compares the mechanism of replication initiation in yeast and mammalian cells, summarizes the sequencing-based technologies used for the identification of initiation sites/zones, and proposes a possible mechanism of initiation-site/zone selection in mammalian cells. Future directions and challenges in this field are also discussed.
摘要：
真核DNA复制是一个严格控制的过程，发生在两个主要步骤，即，许可和解雇，发生在细胞周期的G1和S期，分别。在酿酒酵母中，萌芽酵母，复制起点包含由许可因子Orc1-6识别和结合的共有序列，然后招募复制型Mcm2-7解旋酶。相比之下,哺乳动物起始位点缺乏这种共有序列，并且哺乳动物ORC不表现出序列特异性。过去几十年来进行的研究已经使用基于测序的测定法确定了哺乳动物基因组中的复制起始位点。提出了一个问题，即复制起始是否发生在整个基因组的狭窄位点或广阔区域。尽管最近的报道表明，哺乳动物细胞中获得许可的MCM广泛分布，表明ORC相关的许可可能无法确定启动站点/区域，它们主要位于活跃转录基因的上游。这篇综述比较了酵母和哺乳动物细胞的复制起始机制。总结了用于识别起始位点/区域的基于测序的技术，并提出了哺乳动物细胞中起始位点/区域选择的可能机制。还讨论了该领域的未来方向和挑战。
