Weaver Keith E, Kwong Stephen M, Firth Neville, Francia Maria Victoria
Division of Basic Biomedical Sciences, Sanford School of Medicine, University of South Dakota, Vermillion, SD 57069, USA.
Plasmid. 2009 Mar;61(2):94-109. doi: 10.1016/j.plasmid.2008.11.004. Epub 2009 Jan 6.
The pheromone-responsive conjugative plasmids of Enterococcus faecalis and the multiresistance plasmids pSK1 and pSK41 of Staphylococcus aureus are among the best studied plasmids native to Gram-positive bacteria. Although these plasmids seem largely restricted to their native hosts, protein sequence comparison of their replication initiator proteins indicates that they are clearly related. Homology searches indicate that these replicons are representatives of a large family of plasmids and a few phage that are widespread among the low G+C Gram-positive bacteria. We propose to name this family the RepA_N family of replicons after the annotated conserved domain that the initiator protein contains. Detailed sequence comparisons indicate that the initiator protein phylogeny is largely congruent with that of the host, suggesting that the replicons have evolved along with their current hosts and that intergeneric transfer has been rare. However, related proteins were identified on chromosomal regions bearing characteristics indicative of ICE elements, and the phylogeny of these proteins displayed evidence of more frequent intergeneric transfer. Comparison of stability determinants associated with the RepA_N replicons suggests that they have a modular evolution as has been observed in other plasmid families.
粪肠球菌的信息素响应接合质粒以及金黄色葡萄球菌的多抗性质粒pSK1和pSK41是革兰氏阳性菌中研究得最为深入的天然质粒。尽管这些质粒似乎在很大程度上局限于其天然宿主，但对其复制起始蛋白的蛋白质序列比较表明它们明显相关。同源性搜索表明，这些复制子是一大类质粒和一些噬菌体的代表，它们在低G+C含量的革兰氏阳性菌中广泛存在。我们建议根据起始蛋白所含的注释保守结构域，将这个家族命名为RepA_N复制子家族。详细的序列比较表明，起始蛋白系统发育在很大程度上与宿主的系统发育一致，这表明复制子是与其当前宿主共同进化的，并且属间转移很少见。然而，在具有ICE元件特征的染色体区域上鉴定出了相关蛋白，并且这些蛋白的系统发育显示出更频繁的属间转移的证据。与RepA_N复制子相关的稳定性决定因素的比较表明，它们具有模块化进化，这在其他质粒家族中也有观察到。
