Molecular evolution of recombinational mechanism

RecA蛋白在基因重组过程中起着核心作用，在大多数生物体内高度保守。RecA类重组蛋白参与了基因重组和DNA复制，但其结构和功能关系尚不明确。为了阐明古细菌、原核生物和真核生物进化分化的RecA样蛋白之间的关系，我们克隆了它们的RecA同源基因。嗜热菌的recA/RAD51基因克隆了共同的中心区。它们表现出DNA链交换活性和DNA依赖的ATPase活性，这是同源重组的基本特征。在75ﾟC时，部分RADA蛋白出现阿累尼乌斯曲线断裂，75ﾟ℃以上时，RADA蛋白与单链DNA结合能力和三磷酸腺苷的协同作用较大，而该温度以上的RADA蛋白的水解活化能较低。这些结果表明，这种高温RADA以两种不同的构象存在，其临界温度为75ﾟC。

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.