Antitoxin component of a type II toxin-antitoxin (TA) system. A probable antitoxin for the putative mRNA interferase RelK. Upon expression in E.coli but not in M.smegmatis this protein neutralizes E.coli YoeB. Binds to and represses its own promoter, in combination with RelK repression is somewhat lessened. Several DNA-protein complexes are formed in vitro depending on the RelJ:RelK ratio. Homodimer (Probable). May form RelJ(2)-RelK toxin-antitoxin complexes, in which the toxin is probably inactive. Expressed in log phase cells. A member of the relJK operon. Belongs to the phD/YefM antitoxin family.