State Key Laboratory of Membrane Biology, Peking-Tsinghua Center for Life Sciences, School of Life Sciences, Peking University, Beijing, China.
Division of Life Science, The Hong Kong University of Science and Technology, Hong Kong, China.
Nature. 2018 Jul;559(7713):217-222. doi: 10.1038/s41586-018-0293-x. Epub 2018 Jul 4.
The six-subunit origin recognition complex (ORC) binds to DNA to mark the site for the initiation of replication in eukaryotes. Here we report a 3 Å cryo-electron microscopy structure of the Saccharomyces cerevisiae ORC bound to a 72-base-pair origin DNA sequence that contains the ARS consensus sequence (ACS) and the B1 element. The ORC encircles DNA through extensive interactions with both phosphate backbone and bases, and bends DNA at the ACS and B1 sites. Specific recognition of thymine residues in the ACS is carried out by a conserved basic amino acid motif of Orc1 in the minor groove, and by a species-specific helical insertion motif of Orc4 in the major groove. Moreover, similar insertions into major and minor grooves are also embedded in the B1 site by basic patch motifs from Orc2 and Orc5, respectively, to contact bases and to bend DNA. This work pinpoints a conserved role of ORC in modulating DNA structure to facilitate origin selection and helicase loading in eukaryotes.
六亚基起始识别复合物（ORC）与 DNA 结合，以标记真核生物中复制起始的位点。在这里，我们报道了酿酒酵母 ORC 与包含 ARS 保守序列（ACS）和 B1 元件的 72 碱基对起始 DNA 序列结合的 3Å 冷冻电镜结构。ORC 通过与磷酸骨架和碱基的广泛相互作用环绕 DNA，并在 ACS 和 B1 位点使 DNA 弯曲。ACS 中胸腺嘧啶残基的特异性识别由 Orc1 的保守碱性氨基酸基序在小沟中完成，由 Orc4 的种特异性螺旋插入基序在大沟中完成。此外，Orc2 和 Orc5 的基本斑块基序分别将类似的插入到大沟和小沟中，以与碱基接触并使 DNA 弯曲，从而嵌入 B1 位点。这项工作指出了 ORC 在调节 DNA 结构以促进真核生物中原点选择和解旋酶加载中的保守作用。
