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首页> 外文期刊>Journal of bacteriology >Repression of the traM gene of plasmid R100 by its own product and integration host factor at one of the two promoters.
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Repression of the traM gene of plasmid R100 by its own product and integration host factor at one of the two promoters.

机译：质粒R100的traM基因在两个启动子之一处被其自身产物和整合宿主因子抑制。

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Plasmid R100 codes for the traM gene, which is required for DNA transfer and whose product has been shown to bind to the four sites, called sbmA to sbmD, upstream of traM. To determine whether the TraM protein regulates the expression of traM, we constructed the plasmids carrying various portions of the region upstream of the initiation codon ATG for traM, which was fused with lacZ in frame, and introduced them into the cells, which did or did not harbor another compatible plasmid carrying traM. We then assayed the beta-galactosidase (LacZ) activity to monitor the expression of the fusion genes and analyzed the traM-specific transcripts made in the cells. Two promoters for traM were identified and designated pM1 and pM2. Promoter pM2 lies upstream of pM1 and overlaps the sbmC-sbmD region. Promoter pM1 is constitutively expressed, while pM2 is much stronger but is repressed almost completely by the TraM protein and partially by integration host factor, whose binding site is near pM2. The traM gene is likely to be expressed from pM2 when the TraM protein is at low levels after dilution in the donor cell during cell growth or before its expression in the recipient cell which has just received R100 by conjugation. The expression from pM2 could maintain the amount of the TraM protein at a constant level needed to initiate DNA transfer at any time. Integration host factor, which can partially repress the traM gene, may play a role in forming an active complex with the TraM protein at the sbm region to facilitate DNA transfer.
机译：质粒R100编码traM基因，这是DNA转移所必需的，其产物已显示与traM上游的四个位点sbmA到sbmD结合。为了确定TraM蛋白是否调节traM的表达，我们构建了携带traM起始密码子ATG上游区域各部分的质粒，将其与lacZ框内融合，然后将它们引入细胞中。没有携带另一种携带traM的兼容质粒。然后，我们分析了β-半乳糖苷酶（LacZ）活性以监测融合基因的表达，并分析了细胞中产生的traM特异性转录物。确定了traM的两个启动子，分别命名为pM1和pM2。启动子pM2位于pM1的上游，并与sbmC-sbmD区域重叠。启动子pM1是组成型表达的，而pM2则更强，但几乎完全被TraM蛋白和部分被结合位点靠近pM2的整合宿主因子抑制。当TraM蛋白在细胞生长过程中在供体细胞中稀释后或在其通过结合刚接受R100的受体细胞中表达之前处于较低水平时，traM蛋白很可能从pM2表达。来自pM2的表达可以将TraM蛋白的量维持在随时启动DNA转移所需的恒定水平。可以部分抑制traM基因的整合宿主因子可能在sbm区域与TraM蛋白形成活性复合物以促进DNA转移中发挥作用。

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