Probable antitoxin component of a putative type VII toxin-antitoxin (TA) system. Neutralizes cognate toxic MJ0127 by di-AMPylation. ATP + L-tyrosyl-[protein] = diphosphate + O-(5'-adenylyl)-L-tyrosyl-[protein] ATP + O-(5'-adenylyl)-L-tyrosyl-[protein] = diphosphate + O-[5'-(adenylyl-(5'->3')-adenylyl)]-L-tyrosyl-[protein] Binds 2 Mg(2+) ions. Probably forms a complex with cognate toxin MJ0127. Belongs to the MntA antitoxin family.