Molecular evolution of recombinational mechanism

RecA蛋白在基因重组过程中起着核心作用，并且在大多数生物体中高度保守。RecA-like重组蛋白参与基因重组和DNA复制，但其结构与功能关系尚不清楚。为了阐明古生菌、原核生物和真核生物中进化趋异的RecA类蛋白之间的关系，我们克隆了它们的RecA同源物，其中嗜热菌的recA/RAD 51基因克隆了共有的中心区域。它们表现出DNA链交换活性和依赖于DNA的ATP酶活性，这是同源重组的基本特性。某些RecA蛋白在有DNA和无DNA的条件下都能结晶，有些RadA蛋白在75 ℃时ATP水解的Arrhenius曲线出现断裂，在75 ℃以上，其ATP水解的相关性和单链DNA结合能力比低温时大，而在此断裂点以上，ATP水解的活化能较低。这些结果表明，这种超嗜热RadA存在于两种不同的构象，与75 ℃的临界温度。

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.