Conjugal transfer of plasmid pMV158: uncoupling of the pMV158 origin of transfer from the mobilization gene mobM, and modulation of pMV158 transfer in Escherichia coli mediated by IncP plasmids

The streptococcal plasmid pMV158 encodes a gene cassette involved in its mo bilization by targe conjugative plasmids. Two elements compose this region: i) the mobM gene, encoding the MobM protein that initiates transfer, and i i) the origin of transfer, oriT, which is the target of MobM. In vitro, Mob M protein introduces a specific nick within the pMV158-oriT region on super coiled pMV158 DNA. This paper reports the uncoupling of the oriT and the mo bM gene, the latter being placed under the control of an inducible promoter . Upon induction, the vector containing pMV158-oriT was transferred in Esch erichia coil matings at a moderate frequency whereas, in vitro, purified Mo bM protein efficiently cleaved the vector harbouring the pMV158-oriT. Trans fer of this vector, as well as transfer of pMV158 in E. coil, required the presence of either the IncW R388 or the IncP 884 plasmids as auxiliary plas mids. Dissection of the functions encoded by RP4 showed that the traG and t raF genes were essential for pMV158 mobilization.