Conjugative DNA transfer (CDT) is the unidirectional transfer of ssDNA plasmid from a donor to a recipient cell. It is the central mechanism by which antibiotic resistance and virulence factors are propagated in bacterial populations. Couples the transferosome to a type IV secretion system. Probably forms a pore through which single-stranded plasmid DNA is transferred to the secretion system. The last 37 residues are important for determining plasmid specificity and transfer efficiency, with additional specificity conferred by the TraD-TraM pair. Interacts with relaxosome component TraM. May form a hexamer in the membrane. Belongs to the TrwB coupling protein family. Extended C-terminus.