Molecular evolution of recombinational mechanism

RecA蛋白在基因重组过程中起核心作用，在大多数生物体中高度保守。reca样重组蛋白参与基因重组和DNA复制，但其结构和功能关系尚不清楚。为了阐明古生物、原核生物和真核生物中进化差异的RecA样蛋白之间的关系，我们克隆了它们的RecA同源蛋白。嗜热细菌的recA/RAD51基因克隆了共同的中心区域。它们具有DNA链交换活性和DNA依赖性atp酶活性，这是同源重组的基本特性。一些嗜热的RecA蛋白可以在有DNA和没有DNA的情况下结晶。部分RadA蛋白在75℃时出现ATP水解阿伦尼乌斯图断裂。在75ºC以上，蛋白的ATP水解协同性和单链DNA结合能力均高于较低温度，而在75ºC以上ATP水解活化能较低。结果表明，该超嗜热RadA存在两种不同的构象，其临界温度为75℃。

The RecA protein plays the central role in the process of genetic recombination and is highly conserved in most living organisms. The RecA-like recombinational proteins are involved in genetic recombination and DNA replication, but the structure and function relationship is still uncertain. In order to elucidate the relationship among evolutionary divergent RecA-like proteins of archea, prokaryotes and eukaryotes, we cloned their RecA homologes.The recA/RAD51 gene of thermophilic bacteria had cloned common central regions. They showed DNA strand-exchange activities and DNA-dependent ATPase activities, which are essential properties of homologous recombination. Some thermophilic RecA proteins could be crystallized with and without DNA.Some RadA protein exhibited a break in the Arrhenius plot of ATP hydrolysis at 75ﾟC.The coperativity of ATP hydrolysis and single-stranded DNA binding ability of the protein above 75ﾟC were larger than those at lower temperatures, while the activation energy of ATP hydrolysis was lower above this break point temperature. These results suggest that this hyperthermophilic RadA exists in two different conformations, with 75ﾟC being the critical temperature.