Margolin W, Long S R
Department of Biological Sciences, Stanford University, California 94305-5020.
J Bacteriol. 1994 Apr;176(7):2033-43. doi: 10.1128/jb.176.7.2033-2043.1994.
We have identified a second homolog of the cell division gene, ftsZ, in the endosymbiont Rhizobium meliloti. The ftsZ2 gene was cloned by screening a genomic lambda library with a probe derived from PCR amplification of a highly conserved domain. It encodes a 36-kDa protein which shares a high level of sequence similarity with the FtsZ proteins of Escherichia coli and Bacillus subtilis and FtsZ1 (Z1) of R. meliloti but lacks the carboxy-terminal region conserved in other FtsZ proteins. The identity of the ftsZ2 gene product was confirmed both by in vitro transcription-translation in an R. meliloti S-30 extract and by overproduction in R. meliloti cells. As with Z1, the overproduction of FtsZ2 in E. coli inhibited cell division and induced filamentation, although to a lesser extent than with Z1. However, the expression of ftsZ2 in E. coli under certain conditions caused some cells to coil dramatically, a phenotype not observed during Z1 overproduction. Although several Tn3-GUS (glucuronidase) insertions in a plasmid-borne ftsZ2 gene failed to cross into the chromosome, one interruption in the chromosomal ftsZ2 gene was isolated, suggesting that ftsZ2 is nonessential for viability. The two ftsZ genes were genetically mapped to the R. meliloti main chromosome, approximately 100 kb apart.
我们在共生菌苜蓿中华根瘤菌（Rhizobium meliloti）中鉴定出了细胞分裂基因ftsZ的第二个同源物。通过用源自高度保守结构域PCR扩增的探针筛选基因组λ文库，克隆出了ftsZ2基因。它编码一种36 kDa的蛋白质，该蛋白质与大肠杆菌和枯草芽孢杆菌的FtsZ蛋白以及苜蓿中华根瘤菌的FtsZ1（Z1）具有高度的序列相似性，但缺少其他FtsZ蛋白中保守的羧基末端区域。ftsZ2基因产物的身份通过在苜蓿中华根瘤菌S-30提取物中的体外转录-翻译以及在苜蓿中华根瘤菌细胞中的过量表达得到了证实。与Z1一样，在大肠杆菌中过量表达FtsZ2会抑制细胞分裂并诱导丝状体形成，尽管程度比Z1小。然而，在某些条件下，ftsZ2在大肠杆菌中的表达会导致一些细胞剧烈卷曲，这是在过量表达Z1时未观察到的表型。尽管质粒携带的ftsZ2基因中的几个Tn3-GUS（葡糖醛酸酶）插入未能进入染色体，但分离到了染色体ftsZ2基因中的一个中断，这表明ftsZ2对生存力不是必需的。这两个ftsZ基因在苜蓿中华根瘤菌主染色体上进行了遗传定位，相距约100 kb。
