Genetic organization of a DNA-processing region required for mobilization of a non-self-transmissible plasmid, pEC3, isolated from Erwinia carotovora subsp. carotovora

A non-self-transmissible multiple-copy plasmid, pEC3, isolated from the phytopathogenic bacterium, Erwinia carotovora subsp. carotovora, can be mobilized by an IncP-type plasmid. The hybrid plasmid vector, pETC3, constructed from pEC3 by fusion to markers conferring TC(R) and Cm(R), was transferred by conjugation from Escherichia coli (Ec) to various genera of Enterobacteriaceae and to other genera of Gram^- bacteria which included Xanthomonas, Agrobacterium and Rhizobium. Deletion analysis and successive subcloning of pEC3 revealed that a cis-acting locus, oriT and a trans-acting locus, mob, were involved in mobilization of pEC3. Five open reading frames (ORFs) were found in the mob region, of which four were identified as mobA, B, C and D. The mobA gene overlapped with mobC, B, D and ORF1 that were transcribed polycistronically from upstream from mobC. The nature of the four products of mob genes, MobA, B, C and D, was verified by use of the T7 promoter system in Ec.