Relaxase involved in plasmid ColE1 conjugative mobilization and is thus essential to promote the specific transfer of the plasmid during conjugation. First catalyzes the specific cleavage of one of the DNA strands at oriT, forming a covalent 5'-phosphotyrosine intermediate. The nic site corresponds to 5'-(1469)CTGG/CTTA(1462)-3' in the cleaved strand. The cleaved strand is then transferred through the dedicated type IV secretion apparatus. MbeA remains covalently linked at the 5' end of the strand, and once in the recipient cell, it probably catalyzes the rejoining of the two ends of the strand, re-forming the circular plasmid DNA. Is functional in vitro without a requirement for the conjugative accessory proteins. ATP-independent breakage of single-stranded DNA, followed by passage and rejoining. Divalent metal cation. Can use Mg(2+), Co(2+) or Ni(2+) with similar efficiencies, but is not active in the presence of Mn(2+). Interacts with MbeB and MbeC to form the relaxosome. The 100 C-terminal amino acids are dispensable for activity. To E.coli MbaA and MbkA.