TraG from RP4 and TraG and VirD4 from Ti plasmids confer relaxosome specificity to the conjugal transfer system of pTiC58
TraG from RP4 and TraG and VirD4 from Ti plasmids confer relaxosome specificity to the conjugal transfer system of pTiC58
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DOI：
10.1128/jb.182.6.1541-1548.2000
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发表时间：
2000-03-01
影响因子：
3.2
通讯作者：
Farrand, SK
中科院分区：
文献类型：
--
作者：
Hamilton, CM;Lee, H;Farrand, SK
质粒接合系统由两部分组成，DNA转移和复制系统，或DNA转移和复制系统，或交配对形成系统，或MPF。在配偶转移过程中，一种称为偶联蛋白的基本因子被认为以松弛小体的形式与MPF以交配桥的形式连接在一起。这些蛋白质，如来自IncP1质粒Rp4(Trag(Rp4))的Trag，以及来自钛质粒的配偶转移和T-DNA转移系统的Trag和VirD4，被认为决定了不同DtR和MPF成分之间相互作用的特异性。根癌农杆菌的Ti质粒不能动员含有Rp4 ORIT的载体，但这些IncP1质粒衍生物缺乏反式作用的Dtr功能和Trag(Rp4)。以根癌农杆菌为供体，构建了含有Rp4的ORIT、DTR基因和pTiC58的MPF基因的嵌合表达载体，表明钛质粒交配桥可以与Rp4松弛小体相互作用。然而，钛质粒不能动员INQ松弛小体的转移。如果TRAG(Rp4)在供体中表达，则钛质粒确实动员了这些质粒。对Rp4转移系统有明确影响的Trag(Rp4)突变在钛质粒介导的incq载体动员中表现出相似的表型。当提供VirD4时，pTiC58的反式系统从incq松弛小体中动员了质粒。然而，Trag(Rp4)和VirD4都不能恢复转移到Ti质粒的Trag突变体。VirD4也未能补充Trag(Rp4)突变体，以从Rp4松弛小体转移或Rp4介导的动员从incq松弛小体。TRAG(Rp4)介导的INQ载体被pTiC58动员后不能抑制钛载体的转移，提示两种载体的松弛小体并不竞争同一交配桥。我们的结论是，Trag(Rp4)和VirD4将INQ而不是钛质粒弛豫体偶联到钛质粒交配桥。然而，VirD4不能将IncP1或incq弛豫体偶联到Rp4交配桥。这些结果支持一个模型，在该模型中，偶联蛋白指定交配系统的DtR和MPF组件之间的相互作用。
Plasmid conjugation systems are composed of two components, the DNA transfer and replication system, or Dtr, and the mating pair formation system, or Mpf. During conjugal transfer an essential factor, called the coupling protein, is thought to interface the Dtr, in the form of the relaxosome, with the Mpf, in the form of the mating bridge. These proteins, such as TraG from the IncP1 plasmid RP4 (TraG(RP4)) and TraG and VirD4 from the conjugal transfer and T-DNA transfer systems of Ti plasmids, are believed to dictate specificity of the interactions that can occur between different Dtr and Mpf components. The Ti plasmids of Agrobacterium tumefaciens do not mobilize vectors containing the oriT of RP4, but these IncP1 plasmid derivatives lack the trans-acting Dtr functions and TraG(RP4). A. tumefaciens donors transferred a chimeric plasmid that contains the oriT and Dtr genes of RP4 and the Mpf genes of pTiC58, indicating that the Ti plasmid mating bridge can interact with the RP4 relaxosome. However, the Ti plasmid did not mobilize transfer from an IncQ relaxosome. The Ti plasmid did mobilize such plasmids if TraG(RP4) was expressed in the donors. Mutations in traG(RP4) with defined effects on the RP4 transfer system exhibited similar phenotypes for Ti plasmid-mediated mobilization of the IncQ vector. When provided with VirD4, the tra system of pTiC58 mobilized plasmids from the IncQ relaxosome. However, neither TraG(RP4) nor VirD4 restored transfer to a traG mutant of the Ti plasmid. VirD4 also failed to complement a traG(RP4) mutant for transfer from the RP4 relaxosome or for RP4-mediated mobilization from the IncQ relaxosome. TraG(RP4)-mediated mobilization of the IncQ plasmid by pTiC58 did not inhibit Ti plasmid transfer, suggesting that the relaxosomes of the two plasmids do not compete for the same mating bridge. We conclude that TraG(RP4) and VirD4 couples the IncQ but not the Ti plasmid relaxosome to the Ti plasmid mating bridge. However, VirD4 cannot couple the IncP1 or the IncQ relaxosome to the RP4 mating bridge. These results support a model in which the coupling proteins specify the interactions between Dtr and Mpf components of mating systems.