Probable DNA relaxase involved in the transfer of the integrative and conjugative element ICEBs1. Required for the transfer of ICEBs1. Probably mediates conjugation of ICEBs1 by nicking at oriT on the conjugative element and facilitates the translocation of a single strand of ICEBs1 DNA through a transmembrane conjugation pore into the recipient cell. The oriT nick site is located within the nicK open reading frame. Belongs to the plasmid replication initiation factor family.