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. Part of the relaxosome, which facilitates a site- and strand-specific cut in the origin of transfer by TraI, at the nic site. Relaxosome formation requires binding of IHF and TraY to the oriT region, which then facilitates binding of TraI relaxase. TraI forms a covalent 5'-phosphotyrosine intermediate linkage to the ssDNA. The transesterified T-strand moves from the donor cell to the recipient cell in a 5'to 3' direction, with the DNA helicase activity of TraI unwinding the DNA. DNA transfer occurs via the conjugative pore (transferosome) an intercellular junction mediated by a type IV secretion system, with TraD providing the means to link the relaxosome to the conjugative pore. The relaxase completes DNA transfer by reversing the covalent phosphotyrosine linkage and releasing the T-strand. TraI has also been identified as DNA helicase I. DNA. helicase I is a potent, highly processive DNA-dependent ATPase, able to unwind about 1.1 kb dsDNA per second in a 5' to 3' manner. ATP-independent breakage of single-stranded DNA, followed by passage and rejoining. ATP + H2O = ADP + H(+) + phosphate Nicking activity (relaxase) is inhibited by bisphosphonates such as the non-competitive inhibitor imidobisphosphate (PNP), etidronic acid (ETIDRO) and clodronic acid (CLODRO). The latter 2 are competitive inhibitors, and are already used clinically to treat bone loss (marketed as Didronel and Bonefos). All 3 compounds also inhibit conjugation and kill F plasmid-containing cells. They are specific to dual tyrosine relaxases such as those found in F and related R conjugative plasmids. Monomer. Part of the relaxosome, a complex composed of plasmid-encodes TraI, TraM, TraY and host-encoded IHF bound to the F plasmid origin of transfer (oriT). Directly contacts coupling protein TraD. Seems to directly contact TraM via its C-terminus. Has 4 domains; the relaxase domain (residues 1-330), an unknown domain (residues 330-990), the helicase domain (residues 990-1450) and the C-terminal domain (1450-1756) which is required for conjugative DNA transfer, possibly via interaction with TraM. Loss of conjugative DNA transfer. To TraI of plasmid IncFII R100. Truncated N-terminus.