Ibáñez M, Alvarez I, Rodríguez-Peña J M, Rotger R
Departamento de Microbiologia II, Facultad de Farmacia, Universidad Complutense, Madrid, Spain.
Gene. 1997 Sep 1;196(1-2):145-58. doi: 10.1016/s0378-1119(97)00220-5.
The multicopy plasmid pFM366 was isolated from a virulent Salmonella enteritidis strain and was found to code for DNA methylase activity (Ibáñez and Rotger, 1993). The present work was aimed at characterizing the genetic organization and functional features of this 5.6 kb plasmid. We found pFM366 almost identical to the plasmid P4 isolated from Shigella sonnei, that encodes the SsoII restriction-modification system (Karyagina et al., 1993), and related to other ColE1-type plasmids. Examination of these plasmids revealed a common organization which suggests they were the result of similar recombinational events. The cytosine methylase of pFM366 is nearly identical to M. SsoII, whereas the gene encoding the restrictase homologous to R. SsoII is truncated and its product is inactive. The expression of the cytosine methylase encoded by pFM366 is strongly affected by deletion of regions located upstream and downstream of its ORF, and is negatively controlled by the rpoS gene in Escherichia coli. The methylase activity encoded by pFM366 induces the SOS response, which could be responsible for the observed delay in the growth of E. coli.
多拷贝质粒pFM366是从一株强毒肠炎沙门氏菌中分离得到的，发现它编码DNA甲基化酶活性（伊瓦涅斯和罗特格，1993年）。本研究旨在对这个5.6 kb质粒的遗传组织和功能特性进行表征。我们发现pFM366与从宋内志贺氏菌中分离得到的编码SsoII限制修饰系统的质粒P4几乎相同（卡里亚吉娜等人，1993年），并且与其他ColE1型质粒相关。对这些质粒的研究揭示了一种共同的组织方式，这表明它们是类似重组事件的结果。pFM366的胞嘧啶甲基化酶与M. SsoII几乎相同，而与R. SsoII同源的限制酶编码基因是截短的，其产物无活性。pFM366编码的胞嘧啶甲基化酶的表达受到其开放阅读框上游和下游区域缺失的强烈影响，并且在大肠杆菌中受到rpoS基因的负调控。pFM366编码的甲基化酶活性诱导SOS反应，这可能是观察到的大肠杆菌生长延迟的原因。
