Morrissey J A, Cashmore A M
Department of Genetics, University of Leicester, UK.
Mol Microbiol. 1992 Nov;6(21):3101-7. doi: 10.1111/j.1365-2958.1992.tb01767.x.
The 2 micrometer plasmid encodes a mechanism that ensures the partitioning of the plasmid at cell division. Little is known about the detailed mechanism of this partitioning system; for example, is there equal or unequal distribution of the plasmid molecules at mitosis? The plasmid also encodes a site-specific recombination system that is thought to be involved in plasmid copy-number amplification, although to date there has been no direct evidence that the recombination process itself is important for maintenance. We have identified a natural 2 micrometer variant that has a cis-acting mutation in the FLP-mediated recombination system. We show that this plasmid is unable to amplify in vivo. Our results demonstrate that the average copy number per cell is not affected for the mutant but there is a large clonal variation. This is a direct demonstration that plasmid partitioning results in an unequal distribution of plasmids and that FLP-mediated amplification compensates for this and therefore has an important role in maintenance.
2 微米质粒编码一种机制，可确保质粒在细胞分裂时进行分配。关于这种分配系统的详细机制知之甚少；例如，在有丝分裂时质粒分子是均等还是不均等分配？该质粒还编码一个位点特异性重组系统，尽管迄今为止尚无直接证据表明重组过程本身对维持质粒很重要，但人们认为它参与了质粒拷贝数的扩增。我们鉴定出一种天然的 2 微米变体，其在 FLP 介导的重组系统中有一个顺式作用突变。我们发现这种质粒在体内无法扩增。我们的结果表明，突变体的每个细胞平均拷贝数不受影响，但存在很大的克隆变异。这直接证明了质粒分配会导致质粒的不均等分布，而 FLP 介导的扩增可对此进行补偿，因此在维持质粒方面具有重要作用。
