Komori K, Sakae S, Shinagawa H, Morikawa K, Ishino Y
Department of Molecular Biology, Biomolecular Engineering Research Institute, Suita, Osaka 565-0874, Japan.
Proc Natl Acad Sci U S A. 1999 Aug 3;96(16):8873-8. doi: 10.1073/pnas.96.16.8873.
The Holliday junction is an essential intermediate of homologous recombination. RecA of Bacteria, Rad51 of Eukarya, and RadA of Archaea are structural and functional homologs. These proteins play a pivotal role in the formation of Holliday junctions from two homologous DNA duplexes. RuvC is a specific endonuclease that resolves Holliday junctions in Bacteria. A Holliday junction-resolving activity has been found in both yeast and mammalian cells. To examine whether the paradigm of homologous recombination apply to Archaea, we assayed and found the activity to resolve a synthetic Holliday junction in crude extract of Pyrococcus furiosus cells. The gene, hjc (Holliday junction cleavage), encodes a protein composed of 123 amino acids, whose sequence is not similar to that of any proteins with known function. However, all four archaea, whose total genome sequences have been published, have the homologous genes. The purified Hjc protein cleaved the recombination intermediates formed by RecA in vitro. These results support the notion that the formation and resolution of Holliday junction is the common mechanism of homologous recombination in the three domains of life.
霍利迪连接体是同源重组的重要中间体。细菌中的RecA、真核生物中的Rad51和古细菌中的RadA是结构和功能上的同源物。这些蛋白质在由两条同源DNA双链形成霍利迪连接体的过程中起关键作用。RuvC是一种特异性核酸内切酶，可在细菌中拆分霍利迪连接体。在酵母和哺乳动物细胞中均发现了霍利迪连接体拆分活性。为了研究同源重组模式是否适用于古细菌，我们进行了检测并发现嗜热栖热菌细胞粗提物中具有拆分合成霍利迪连接体的活性。hjc（霍利迪连接体切割）基因编码一种由123个氨基酸组成的蛋白质，其序列与任何已知功能的蛋白质均不相似。然而，已公布全基因组序列的所有四种古细菌都有同源基因。纯化的Hjc蛋白在体外切割由RecA形成的重组中间体。这些结果支持了霍利迪连接体的形成和拆分是生命三个域中同源重组的共同机制这一观点。
