Structure of the traI-repA intergenic region and of the traI and repA expression clones. Shaded boxes indicate the extents and locations of the conserved tra box elements. Hatched arrows represent the lacZY genes from pLKC482. The vector for pKP19 and pTB12 is pLAFR6; the vector for pPLrep4, -5, and -6 is pJB3. The gene sizes of trbB, traI, repA, and lacZY are not drawn to scale.