Control of initiation of F plasmid replication in Escherichia coli.

严格控制F、mini-F和相关质粒（mini-Rts 1、mini-P1）的复制，以维持它们在每个宿主染色体上的1至2个拷贝数。据认为，质粒拷贝数主要受相应质粒复制所必需的特异性起始蛋白的量或活性调节。我们已经发现编码起始蛋白的mini-F repE基因由含有δ ^的RNA聚合酶转录<32>，并且mini-F不能在缺乏δ ^蛋白的DELTA rpoH细胞中复制<32>。已知大肠杆菌热休克蛋白DnaK、DnaJ和GrpE的一个子集是λ噬菌体DNA复制和大肠杆菌细胞可能在所有温度下生长所需的。我们已经表明，这些热休克蛋白也需要复制的mini-F质粒。当通过携带repE的多拷贝质粒提供过量的复制起始蛋白（RepE）时，mini-F可以在没有DnaK、J、GrpE蛋白的条件下复制。此外，我们已经分离和表征了能够在缺乏δ-γ的情况下复制的mini-F突变体<32>。这些mini-F质粒产生改变的起始蛋白，并表现出非常高的拷贝，并且能够在缺乏任何上述热休克蛋白的菌株中复制。这些结果表明，热休克蛋白的子集发挥重要作用，帮助小F DNA复制中的RepE起始蛋白的功能。我们发现mini-Rts 1和mini-P1样mini-F不能在rpoH菌株中复制。发现这两种质粒的rep基因（如mini-F）都被RNA聚合酶delta^<32>和delta^转录<70>。mini-Rts 1和mini-P1样mini-F的复制也依赖于DnaK、DnaJ和GrpE蛋白。

Replication of F, mini-F and related plasmids ( mini-Rts1, mini-P1 ) is stringently controlled to maintain their copy number of 1 to 2 per host chromosome. It is thought that the plasmid copy number is regulated primarily by the amount or activity of the specific initiator protein essential for replication of the respective plasmid. We have found that the mini-F repE gene encoding the initiator protein is transcribed by RNA polymerase containing delta^<32> and that mini-F can not replicate in DELTA rpoH cells lacking delta^<32> protein. A subset of E.coli heat shock protein DnaK, DnaJ and GrpE are known to be required for lambda phage DNA replication and for growth of E.coli cells probably at all temperature. We have shown that these heat shock proteins are also required for replication of mini-F plasmid. When excess amounts of the replication initiator protein (RepE) were provided by means of a multicopy plasmid carrying repE,mini-F can replicate in the condition without DnaK, J, GrpE protein. Furthermore, we have isolated and characterized mini-F mutants able to replicate in the absence of delta^<32>. These mini-F plasmid produced altered initiator protein and exhibited a very high copy and were able to replicate in strains deficient in any of the above heat shock proteins. These results indicate that the subset of heat shock proteins play essential roles that help the functioning of the RepE initiator protein in mini-F DNA replication. We found that mini-Rts1 and mini-P1 like mini-F cannot replicate in the rpoH strain. The rep genes of both these plasmids like the mini-F were found to be transcribed by RNA polymerase delta^<32> as well as by delta^<70>. The replication of mini-Rts1 and mini-P1 like mini-F also depends on DnaK,DnaJ and GrpE protein.