Putative antitoxin component of a putative type VII toxin-antitoxin (TA) system. Its cognate toxin might be MF0142, which it might AMPylate. 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. Belongs to the MntA antitoxin family.