细胞世界

在减数分裂和同源DNA修复中，会形成一个被称为“霍利迪连结体”(Holliday junction)的四链DNA中间体。这个结构以共价键方式连接两个DNA分子，因此必须将其拆解，才能让染色体正确分离和复制。

1991年，研究人员发现，大肠杆菌中的ruvC基因的产物为细菌“霍利迪连结体”解离酶。不过，哺乳动物相应的酶却并不好寻找，但经过17年之后，它们终于被发现了。人体中的这种酶是一种被称为GEN1的蛋白，酵母中的这种酶是其直系同源蛋白，即Yen 1。二者都是结构特异性核酶的Rad2/XPG家族的成员。



Nature 456, 357-361 (20 November 2008) | doi:10.1038/nature07470

Identification of Holliday junction resolvases from humans and yeast

Stephen C. Y. Ip1,3, Ulrich Rass1,3, Miguel G. Blanco1,3, Helen R. Flynn2, J. Mark Skehel2 & Stephen C. West1

1 Genetic Recombination Laboratory,
2 Protein Analysis and Proteomics Laboratory, Cancer Research UK, London Research Institute, Clare Hall Laboratories, South Mimms, Herts EN6 3LD, UK
3 These authors contributed equally to this work.

Abstract

Four-way DNA intermediates, also known as Holliday junctions, are formed during homologous recombination and DNA repair, and their resolution is necessary for proper chromosome segregation. Here we identify nucleases from Saccharomyces cerevisiae and human cells that promote Holliday junction resolution, in a manner analogous to that shown by the Escherichia coli Holliday junction resolvase RuvC. The human Holliday junction resolvase, GEN1, and its yeast orthologue, Yen1, were independently identified using two distinct experimental approaches: GEN1 was identified by mass spectrometry following extensive fractionation of HeLa cell-free extracts, whereas Yen1 was detected by screening a yeast gene fusion library for nucleases capable of Holliday junction resolution. The eukaryotic Holliday junction resolvases represent a new subclass of the Rad2/XPG family of nucleases. Recombinant GEN1 and Yen1 resolve Holliday junctions by the introduction of symmetrically related cuts across the junction point, to produce nicked duplex products in which the nicks can be readily ligated.