Marks G L, Wood D O
Department of Medicine, University of South Alabama College of Medicine, Mobile 36688.
Gene. 1993 Jan 15;123(1):121-5. doi: 10.1016/0378-1119(93)90550-m.
The gene (dnaG) coding for DNA primase in the obligate intracellular parasitic bacterium, Rickettsia prowazekii, has been isolated and characterized. An open reading frame (ORF) of 1848 bp capable of encoding 616 amino acids (aa) is located 18 bp upstream from the gene coding for the major sigma factor of R. prowazekii, sigma 73. Based on aa sequence comparisons of DNA primase from R. prowazekii, Escherichia coli, Salmonella typhimurium and Bacillus subtilis, we propose that R. prowazekii dnaG begins 69 bp into the ORF and encodes 593 aa with a calculated M(r) of 68,683. An upstream ORF overlaps 66 of the first 69 bp of the larger R. prowazekii dnaG ORF, suggesting either an overlapping gene structure or the generation of the smaller protein product of 593 aa. Predicted aa sequence of R. prowazekii primase compared to E. coli, S. typhimurium and B. subtilis primases reveals 30.5%, 30.5% and 29.7% aa identity, respectively. The R. prowazekii dnaG gene failed to complement an E. coli dnaG temperature sensitive mutation perhaps due to poor expression of the gene or inability to function properly in E. coli. The gene organization of an ORF followed by DNA primase (dnaG) and then the major sigma factor (rpoD) is consistent with the major macromolecular synthesis operons of E. coli, S. typhimurium and B. subtilis.
已分离并鉴定了专性细胞内寄生细菌普氏立克次体中编码DNA引发酶的基因（dnaG）。一个1848 bp的开放阅读框（ORF），能够编码616个氨基酸（aa），位于普氏立克次体主要σ因子σ73编码基因上游18 bp处。基于普氏立克次体、大肠杆菌、鼠伤寒沙门氏菌和枯草芽孢杆菌DNA引发酶的氨基酸序列比较，我们提出普氏立克次体dnaG从ORF内69 bp处开始，编码593个氨基酸，计算的分子量（M(r)）为68,683。一个上游ORF与较大的普氏立克次体dnaG ORF的前69 bp中的66 bp重叠，这表明存在重叠基因结构或产生了593个氨基酸的较小蛋白质产物。与大肠杆菌、鼠伤寒沙门氏菌和枯草芽孢杆菌引发酶相比，普氏立克次体引发酶的预测氨基酸序列分别显示出30.5%、30.5%和29.7%的氨基酸同一性。普氏立克次体dnaG基因未能互补大肠杆菌dnaG温度敏感突变，这可能是由于该基因表达不佳或无法在大肠杆菌中正常发挥功能。一个ORF接着是DNA引发酶（dnaG），然后是主要σ因子（rpoD）的基因组织与大肠杆菌、鼠伤寒沙门氏菌和枯草芽孢杆菌的主要大分子合成操纵子一致。
