Stirling C J, Szatmari G, Stewart G, Smith M C, Sherratt D J
Institute of Genetics, University of Glasgow, UK.
EMBO J. 1988 Dec 20;7(13):4389-95. doi: 10.1002/j.1460-2075.1988.tb03338.x.
The heritable stability in Escherichia coli of the multicopy plasmid ColE1 and its natural relatives requires that the plasmids be maintained in the monomeric state. Plasmid multimers, that arise through recA-dependent homologous recombination, are normally converted to monomers by a site-specific recombination system that acts at a specific plasmid site (cer in ColE1). No plasmid functions that act at this site have been identified. In contrast, two unlinked E.coli genes that encode functions required for cer-mediated site-specific recombination have been identified. Here we describe the isolation and characterization of one such gene (xerA) and show it to be identical to the gene encoding the repressor of the arginine biosynthetic genes (argR). The argR protein binds to cer DNA both in vivo and in vitro in the presence of arginine. We believe this binding is required to generate a higher order protein-DNA complex within the recombinational synapse. The argR gene of Bacillus subtilis complements an E.coli argR deficiency for cer-mediated recombination despite the two proteins having only 27% amino acid identity.
多拷贝质粒ColE1及其天然亲缘质粒在大肠杆菌中的遗传稳定性要求这些质粒保持单体状态。通过recA依赖的同源重组产生的质粒多聚体，通常会被一个位点特异性重组系统转化为单体，该系统作用于特定的质粒位点（ColE1中的cer）。尚未鉴定出在此位点起作用的质粒功能。相反，已经鉴定出两个不连锁的大肠杆菌基因，它们编码cer介导的位点特异性重组所需的功能。在这里，我们描述了其中一个这样的基因（xerA）的分离和特性，并表明它与编码精氨酸生物合成基因（argR）阻遏物的基因相同。在精氨酸存在的情况下，argR蛋白在体内和体外均与cer DNA结合。我们认为这种结合对于在重组突触内产生更高阶的蛋白质-DNA复合物是必需的。尽管枯草芽孢杆菌的argR蛋白与大肠杆菌的argR蛋白只有27%的氨基酸同一性，但它能补充大肠杆菌中cer介导重组所需的argR缺陷。
