FIG. 3.

Genetic structure of pPLtrb-DB. This plasmid, based on the IncP1 vector pJB3 (thin black line) (5), contains the entire trb region from pTiC58 (open arrows) and the Tra1 core region from RP4 (light shaded arrows). traG, which codes for the RP4-coupling protein, is indicated by the dark shaded arrow. oriV, origin of vegetative plasmid replication; trfA, the gene coding for the replication initiation protein of RP4; Amp/Cb, the bla gene coding for resistance to ampicillin and carbenicillin. See Materials and Methods for details.