Coutinho Bruna Gonçalves, Coelho Marcus Lívio Varella, Ceotto Hilana, Bastos Maria do Carmo de Freire
Departamento de Microbiologia Geral, Instituto de Microbiologia Prof. Paulo de Góes, UFRJ, Rio de Janeiro, Brazil.
J Mol Microbiol Biotechnol. 2011;21(3-4):173-83. doi: 10.1159/000335356. Epub 2012 Jan 31.
Plasmid pRJ9 is a non-self-mobilizable bacteriocinogenic plasmid from Staphylococcus aureus. Despite this feature, DNA sequencing and RT-PCR experiments showed that it presents a Mob region with three genes (mobCAB), transcribed as an operon. In silico analysis of the Mob proteins encoded by pRJ9 showed that they present all the conserved functional features reported until present as being essential for plasmid mobilization. Moreover, they showed a high identity to Mob proteins encoded by mobilizable plasmids from Staphylococcus spp., especially to those encoded by plasmid pRJ6, which presents four mob genes (mobCDAB). A putative oriT region was also found upstream of the pRJ9 mob operon. pRJ9 could only be successfully mobilized by pGO1 when pRJ6 was present in the same strain. Further experiments showed that the pRJ9 oriT can be recognized by the pRJ6 Mob proteins, confirming its functionality. As pRJ9 does not possess a mobD gene while pRJ6 does, the absence of this gene was believed to be responsible for its lack of mobilization. However, conjugation experiments with a donor strain carrying also mobD cloned into an S. aureus vector showed that pRJ9 does not become mobilized even in the presence of the protein MobD encoded by pRJ6. Therefore, the reasons for pRJ9 failure to be mobilized are presently unknown.
质粒pRJ9是一种来自金黄色葡萄球菌的非自我转移性产细菌素质粒。尽管有此特性，但DNA测序和逆转录聚合酶链反应实验表明，它有一个包含三个基因（mobCAB）的Mob区域，转录为一个操纵子。对pRJ9编码的Mob蛋白进行的电子分析表明，它们具有目前报道的对质粒转移至关重要的所有保守功能特征。此外，它们与葡萄球菌属可移动质粒编码的Mob蛋白具有高度同一性，特别是与质粒pRJ6编码的Mob蛋白，pRJ6有四个mob基因（mobCDAB）。在pRJ9的mob操纵子上游还发现了一个假定的oriT区域。只有当pRJ6存在于同一菌株中时，pRJ9才能被pGO1成功转移。进一步的实验表明，pRJ9的oriT可以被pRJ6的Mob蛋白识别，证实了其功能。由于pRJ9不具有mobD基因而pRJ具有，因此认为该基因的缺失是其缺乏转移能力的原因。然而，用携带克隆到金黄色葡萄球菌载体中的mobD的供体菌株进行的接合实验表明，即使存在pRJ6编码的MobD蛋白，pRJ9也不会被转移。因此，目前尚不清楚pRJ9不能被转移的原因。
