Conley D L, Cohen S N
Department of Genetics, Stanford University School of Medicine, California 94305.
J Bacteriol. 1995 Feb;177(4):1086-9. doi: 10.1128/jb.177.4.1086-1089.1995.
Second-site mutations that allow stable inheritance of partition-defective pSC101 plasmids mapped to seven distinct sites in the 5' half of the plasmid repA gene. While the mutations also elevated pSC101 copy number, there was no correlation between copy number increase and plasmid stability. Combinations of mutations enabled pSC101 DNA replication in the absence of integration host factor and also stabilized par-deleted plasmids in cells deficient in DNA gyrase or defective in DnaA binding. Our findings suggest that repA mutations compensate for par deletion by enabling the origin region RepA-DNA-DnaA complex to form under suboptimal conditions. They also provide evidence that this complex has a role in partitioning that is separate from its known ability to promote plasmid DNA replication.
能够使分区缺陷型pSC101质粒稳定遗传的第二位点突变定位于质粒repA基因5'端的七个不同位点。虽然这些突变也提高了pSC101的拷贝数，但拷贝数增加与质粒稳定性之间没有相关性。突变组合能够使pSC101 DNA在没有整合宿主因子的情况下进行复制，并且还能在缺乏DNA促旋酶或DnaA结合有缺陷的细胞中稳定缺失par的质粒。我们的研究结果表明，repA突变通过使起始区域的RepA-DNA-DnaA复合物在次优条件下形成来补偿par缺失。它们还提供了证据，证明这种复合物在分区中具有与其已知的促进质粒DNA复制的能力不同的作用。
