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首页> 外文期刊>Journal of bacteriology >Processed VirB2 Is the Major Subunit of the Promiscuous Pilus of Agrobacterium tumefaciens
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Processed VirB2 Is the Major Subunit of the Promiscuous Pilus of Agrobacterium tumefaciens

机译：加工过的VirB2是根癌农杆菌杂菌的主要亚基。

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Previous studies have implicated the obligatory requirement for thevir regulon (or “virulon”) of the Ti plasmid for the transfer of oncogenes from Agrobacterium tumefaciens to plant cells. The machinery used in this horizontal gene transfer has been long thought to be a transformation or conjugative delivery system. Based on recent protein sequence comparisons, the proteins encoded by the virB operon are strikingly similar to proteins involved in the synthesis and assembly of conjugative pili such as the conjugative pilus of F plasmid in Escherichia coli. The F pilus is composed of TraA pilin subunits derived from TraA propilin. In the present study, evidence is provided showing that the counterpart of TraA is VirB2, which like TraA propilin is processed into a 7.2-kDa product that comprises the pilus subunit as demonstrated by biochemical and electron microscopic analyses. The processed VirB2 protein is present exocellularly on medium on which induced A. tumefaciens had grown and appears as thin filaments of 10 nm that react specifically to VirB2 antibody. Exocellular VirB2 is produced abundantly at 19°C as compared with 28°C, an observation that parallels the effect of low temperature on the production ofvir gene-specific pili observed previously (K. J. Fullner, L. C. Lara, and E. W. Nester, Science 273:1107–1109, 1996). Export of the processed VirB2 requires othervirB genes since mutations in these genes cause the loss of VirB2 pilus formation and result in processed VirB2 accumulation in the cell. The presence of exocellular processed VirB2 is directly correlated with the formation of pili, and it appears as the major protein in the purified pilus preparation. The evidence provides a compelling argument for VirB2 as the propilin whose 7.2-kDa processed product is the pilin subunit of the promiscuous conjugative pilus, hereafter called the “T pilus” of A. tumefaciens.
机译：以前的研究表明，Ti质粒的 vir regulon（或“ virulon”）对于将癌基因从根癌农杆菌转移到植物细胞的强制性要求。长期以来，这种水平基因转移中使用的机制一直被认为是转化或结合递送系统。根据最近的蛋白质序列比较， virB 操纵子编码的蛋白质与参与结合菌毛的合成和组装的蛋白质非常相似，例如 Ecocherichia coli < / em>。 F菌毛由衍生自TraA丙蛋白的TraA菌毛素亚基组成。在本研究中，提供的证据表明TraA的对应物是VirB2，如生物化学和电子显微镜分析所示，它与TraA丙脯蛋白一样被加工成包含菌毛亚基的7.2 kDa产物。加工过的VirB2蛋白胞外存在于诱导出 A的培养基上。 tumefaciens 已经生长并以10 nm的细丝出现，与VirB2抗体发生特异性反应。与28°C相比，胞外VirB2在19°C时大量产生，这一观察结果与以前观察到的低温对 vir 基因特异性菌毛产生的影响相类似（KJ Fullner，LC Lara，和EW Nester，《科学》（Science）273：1107-1109，1996）。加工过的VirB2的输出还需要其他 virB 基因，因为这些基因中的突变会导致VirB2菌毛形成的损失，并导致加工后的VirB2在细胞中积累。细胞外加工的VirB2的存在与菌毛的形成直接相关，并且它是纯化菌毛制剂中的主要蛋白质。证据提供了一个令人信服的论点，证明VirB2是一种丙脯蛋白，其7.2 kDa加工产物是混杂共轭菌毛的菌毛素亚基，以下称为 A的“ T菌毛”。肿瘤。

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