Brochet Mathieu, Da Cunha Violette, Couvé Elisabeth, Rusniok Christophe, Trieu-Cuot Patrick, Glaser Philippe
Institut Pasteur, Unité de Génétique des Génomes Bactériens, CNRS URA 2171, France.
Mol Microbiol. 2009 Feb;71(4):948-59. doi: 10.1111/j.1365-2958.2008.06579.x. Epub 2008 Dec 18.
We describe in Streptococcus agalactiae an atypical family of conjugative transposons named TnGBSs which associates DDE transposition and conjugation. We present evidence that the transposition of TnGBS2, the prototype of this family, is catalysed by a new class of DDE transposases that are widespread in Gram-positive bacteria. Remarkably, transposition occurs in intergenic regions, 15 or 16 bp upstream the -35 sequence of promoters, minimizing the burden on the host cell and suggesting an association between transcription and transposition. Transposition catalyses the formation of a circular intermediate that is substrate for subsequent conjugative intercellular transfer. Conjugation is initiated at an origin of transfer by a transposon-encoded relaxase. Whereas all integrative and conjugative elements described so far encode a phage-related integrase, TnGBS2 is the first example of conjugative transposon whose recombination is mediated by a DDE transposase. The combination of DDE transposition with conjugation implies recombination constraints linked to the physical separation of donor and recipient molecules.
我们在无乳链球菌中描述了一个非典型的接合转座子家族，名为TnGBSs，它将DDE转座与接合作用联系在一起。我们提供证据表明，该家族的原型TnGBS2的转座由一类新的DDE转座酶催化，这类转座酶在革兰氏阳性菌中广泛存在。值得注意的是，转座发生在基因间区域，即启动子-35序列上游15或16 bp处，从而将对宿主细胞的负担降至最低，并表明转录与转座之间存在关联。转座催化形成一个环状中间体，该中间体是随后细胞间接合转移的底物。接合作用由转座子编码的松弛酶在转移起始点启动。尽管迄今为止描述的所有整合和接合元件都编码一种与噬菌体相关的整合酶，但TnGBS2是第一个其重组由DDE转座酶介导的接合转座子实例。DDE转座与接合作用的结合意味着与供体和受体分子物理分离相关的重组限制。
