Scheme of triparental matings. Bacteria are represented by ovals containing the respective plasmids. Antibiotic resistance of strains and mobilizable plasmids is indicated. Plasmid pSU1371, containing R388-oriT, is mobilized from strain 1 by nonmobilizable helper plasmids pET29:trwABC (providing R388 trwA, trwB, and trwC genes) and pKM101Δmob (providing the T4SS). TrwC is represented by a diamond, leading or not the transferred DNA (wavy line) into a recipient cell. TrwC in strain 2 is able or not to complement the R388 mutants (strain 2, left and right, respectively), leading to transconjugants or lack thereof in strain 3 (strain 3 left and right, respectively). Nx, nalidixic acid; Sm, streptomycin; Rf, rifampicin.