Dybvig K, Woodard A
Department of Comparative Medicine, University of Alabama, Birmingham 35294.
J Bacteriol. 1992 Feb;174(3):778-84. doi: 10.1128/jb.174.3.778-784.1992.
Mycoplasmas are wall-less prokaryotes phylogenetically related to gram-positive bacteria. In order to investigate DNA recombination in these organisms, we have cloned the recA gene from the mycoplasma Acholeplasma laidlawii. DNA sequence data indicate extensive homology between the A. laidlawii recA gene and recA genes from other bacteria, particularly Bacillus subtilis. The recA sequences from three A. laidlawii strains (strains JA1, K2, and 8195) were compared, and surprisingly, the gene from A. laidlawii 8195 was found to contain a nonsense mutation that results in truncation of 36 amino acids from the carboxyl terminus of the RecA protein. By using sensitivity to UV irradiation as a measure of DNA repair, strain 8195 had an apparent RecA- phenotype. When carried on a multicopy plasmid, the wild-type A. laidlawii recA gene was detrimental to growth of Escherichia coli, perhaps because of improper regulation of the RecA protein.
支原体是一种无细胞壁的原核生物，在系统发育上与革兰氏阳性菌相关。为了研究这些生物体中的DNA重组，我们从支原体莱氏无胆甾原体中克隆了recA基因。DNA序列数据表明，莱氏无胆甾原体recA基因与其他细菌，特别是枯草芽孢杆菌的recA基因之间存在广泛的同源性。比较了莱氏无胆甾原体三个菌株（JA1、K2和8195菌株）的recA序列，令人惊讶的是，发现来自莱氏无胆甾原体8195的基因含有一个无义突变，该突变导致RecA蛋白羧基末端截短36个氨基酸。以对紫外线照射的敏感性作为DNA修复的指标，8195菌株具有明显的RecA-表型。当携带在多拷贝质粒上时，野生型莱氏无胆甾原体recA基因对大肠杆菌的生长有害，这可能是由于RecA蛋白的调控不当所致。
