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. Plasmid specificity is conferred by the TraD-TraM pair (By similarity). Interacts with relaxosome component TraM. May form a hexamer in the membrane (By similarity). Belongs to the TrwB coupling protein family.