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.The cryo-EM structure of the yeast origin recognition complex (ORC) bound to a 72-base-pair origin DNA sequence provides insights into the basis of the origin selection mechanism.

中文翻译：

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与 DNA 复制起点结合的起点识别复合体的结构

六亚基起源识别复合物 (ORC) 与 DNA 结合以标记真核生物中复制起始的位点。在这里，我们报告了酿酒酵母 ORC 的 3 Å 冷冻电子显微镜结构，该结构与包含 ARS 共有序列 (ACS) 和 B1 元素的 72 碱基对起源 DNA 序列结合。ORC 通过与磷酸骨架和碱基的广泛相互作用包围 DNA，并在 ACS 和 B1 位点弯曲 DNA。ACS 中胸腺嘧啶残基的特异性识别是通过小沟中 Orc1 的保守碱性氨基酸基序和大沟中 Orc4 的物种特异性螺旋插入基序进行的。此外，类似的插入到大沟和小沟中也分别通过 Orc2 和 Orc5 的基本补丁基序嵌入 B1 位点，以接触碱基和弯曲 DNA。