Mortier-Barriere I, Humbert O, Martin B, Prudhomme M, Claverys J P
Laboratoire de Microbiologie et Génétique Moléculaire CNRS-UPR 9007, Université Paul Sabatier, Toulouse, France.
Microb Drug Resist. 1997 Fall;3(3):233-42. doi: 10.1089/mdr.1997.3.233.
Despite the fact that natural transformation was described long ago in Streptococcus pneumoniae, only a limited number of recombination genes have been identified. Two of them have recently been characterized at the molecular level, recA which encodes a protein essential for homologous recombination and mmsA which encodes the homologue of the Escherichia coli RecG protein. After a survey of the available information regarding the function of RecA, RecG, and other proteins such as the mismatch repair proteins HexA and HexB that can affect the outcome of recombinants, the different levels at which horizontal genetic exchange can be controlled are discussed. It is shown that the specific induction of the recA gene which occurs in competent cells is required for full recombination proficiency. Results regarding the ability of the Hex generalized mismatch repair system to prevent recombination between partially divergent sequences during transformation are also summarized. A structural analysis of homeologous recombinants which suggests that formation of mosaic recombinants can occur independently of mismatch repair in a single-step transformation is also reported. Finally, arguments in favor of an evolutionary origin of transformation as a means of genome evolution are discussed and the different types of recombination events observed which could potentially contribute to S. pneumoniae genome evolution are listed.
尽管很久以前就在肺炎链球菌中描述了自然转化，但已鉴定出的重组基因数量有限。其中两个基因最近在分子水平上得到了表征，recA编码同源重组所必需的一种蛋白质，mmsA编码大肠杆菌RecG蛋白的同源物。在对有关RecA、RecG以及其他可能影响重组结果的蛋白质（如错配修复蛋白HexA和HexB）功能的现有信息进行调查之后，讨论了水平基因交换可以被控制的不同层面。结果表明，感受态细胞中recA基因的特异性诱导对于完全的重组能力是必需的。还总结了关于Hex广义错配修复系统在转化过程中阻止部分差异序列之间重组能力的结果。还报道了对同源重组体的结构分析，这表明镶嵌重组体的形成可以在单步转化中独立于错配修复而发生。最后，讨论了支持转化作为基因组进化手段的进化起源的论据，并列出了观察到的可能有助于肺炎链球菌基因组进化的不同类型的重组事件。
