Antitoxin component of a type II toxin-antitoxin (TA) system. Upon expression in M.smegmatis neutralizes the effect of toxin RelE2. Induces its own promoter, in combination with RelG represses its own promoter. Has been seen to bind DNA in complex with toxin RelG but not alone. Interacts with toxin RelG, which neutralizes the toxin. Also interacts with toxins RelE and RelK in vitro, in M.smegmatis coexpression with non-cognate toxins increases the toxicity of RelE but not of RelK. Expressed in log phase cells. Also expressed in human macrophages 110 hours after infection. A member of the relFG operon. Belongs to the phD/YefM antitoxin family.