Cho Hongbaek, Winans Stephen C
Department of Microbiology, Cornell University, Ithaca, NY 14850, USA.
Mol Microbiol. 2007 Mar;63(6):1769-82. doi: 10.1111/j.1365-2958.2007.05624.x.
Whole-genome transcriptional profiling experiments were performed to identify the complete set of TraR-regulated genes in isogenic A. tumefaciens strains containing an octopine-type or nopaline-type Ti plasmid. Most of the known TraR-regulated genes as well as a number of new inducible genes were identified. Surprisingly, some known members of this regulon showed both weaker induction and weak levels of expression than we had predicted based upon earlier studies. In particular, traA was expressed at surprisingly weak levels. Genetic analysis showed that the traAFBH operon is repressed by formation of a putative relaxosome at oriT consisting the TraA, TraC and TraD. These proteins also repressed the divergent traCDGyci operon. TraA was essential for oriT processing, and both TraC and TraD were necessary for the efficient processing, although some processing occurred in their absence. Likewise, Ti plasmid conjugation required TraA, TraF and TraG, and occurred at reduced levels in the absence of TraC or TraD. TraA preferentially acted in cis in repressing the traA and traC promoters and in the processing of oriT, which explains the very high activity of plasmid-borne traA-lacZ fusions reported in previous studies.
进行了全基因组转录谱分析实验，以鉴定携带章鱼碱型或胭脂碱型Ti质粒的同基因根癌土壤杆菌菌株中TraR调控基因的完整集合。鉴定出了大多数已知的TraR调控基因以及一些新的可诱导基因。令人惊讶的是，与我们基于早期研究预测的情况相比，该调控子的一些已知成员表现出较弱的诱导和较低的表达水平。特别是，traA的表达水平出奇地低。遗传分析表明，traAFBH操纵子被在oriT处形成的假定松弛体所抑制，该松弛体由TraA、TraC和TraD组成。这些蛋白质还抑制了反向的traCDGyci操纵子。TraA对于oriT加工至关重要，TraC和TraD对于高效加工都是必需的，尽管在它们缺失时也会发生一些加工。同样，Ti质粒接合需要TraA、TraF和TraG，并且在缺失TraC或TraD时接合水平降低。TraA在抑制traA和traC启动子以及oriT加工中优先以顺式作用，这解释了先前研究中报道的质粒携带的traA - lacZ融合体的非常高的活性。
