Screaning of E.coli Genes That Participate in the Partitioning of F Plasmid DNA

F质粒的LetA(Ccda)和letD(Ccdb)基因位于复制所必需的序列之外，有助于在大肠杆菌细胞中稳定地维持该质粒。LetD基因产物通过直接相互作用使DNA旋转酶的A亚单位失活，从而抑制染色体DNA的分裂和细胞分裂，而letA基因产物则逆转letD基因产物的抑制活性。为了确定参与这一过程的寄主因子(S)，我们分析了这些逃脱letD产物生长抑制和它们的抑制子的突变体，发现除了我们先前报道的GroE基因外，还有三个大肠杆菌基因tldD、tldE和zfiA参与其中。TldD和tldE突变使细胞耐受letD产生生长抑制，而zfiA基因突变使tldD、tldE和groes突变letD敏感。我们假设这些基因产物与letD基因产物一起是调节DNA旋转酶活性的因子；zfiA基因产物抑制letD蛋白与DNA旋转酶A亚基之间的相互作用，而tldD、tldE和zfiA基因产物则抑制zfiA基因产物的抑制活性。TldD、tldE和zfiA基因分别位于大肠杆菌染色体上的70.4、96.0和58.2分钟，编码的蛋白质相对分子质量分别为51,000，48,000和6800。TldD是一个新基因，但tldE和zfiA基因分别被证明是PMBA基因(Microcin B17的产物)和CSRA基因(碳带调节基因)。

The letA (ccdA) and letD (ccdB) genes of the F plasmid, located just outside the sequence essential for replication, contribute to stable maintenance of the plasmid in Escherichia coli cells. The letD gene product acts to inhibit partitioning of chromosomal DNA and cell division by inactivating the A subunit of DNA gyrase by a direct interaction, whereas the letA gene product acts to reverse the inhibitory activity of the letD gene product. To identify the host factor (s) involved in this process, we analyzed such mutants that escaped the letD product growth inhibition and their suppressor, and found that three E.coli genes, tldD,tldE and zfiA participate, in addition to the groE genes we reported previously. tldD and tldE mutations made cells tolerant to the letD product growth inhibition as did groES mutations, while the mutation in the zfiA gene made tldD,tldE and groES mutants letD sensitive. We assume that these gene products are factors that modulate activity of DNA gyrase along with the letD gene product ; zfiA gene product acts to inhibit interaction between the letD protein and the A subunit of DNA gyrase, while the tldD,tldE and zfiA gene products act to suppress the inhibitory activity of the zfiA gene product. The tldD,tldE and zfiA genes are located at 70.4,96.0 and 58.2 minutes on the E coli chromosome, respectively, and code for proteins with relative molecular masses of 51,000,48,000 and 6800, respectively. The tldD is a novel gene, but the tldE and zfiA genes proved to be the pmbA gene (production of Microcin B17) and the csrA gene (carbon strage regulator), respectively.