Probable toxic component of a putative type VII toxin-antitoxin (TA) system, probably an RNase. Probably neutralized by cognate antitoxin MJ0128. Neutralization may be due to AMPylation by MJ0128. Homodimer, probably forms a complex with cognate antitoxin MJ0128. Modified by cognate antitoxin MJ0128; probably at least 2 successive AMPylation events occur on Tyr-83. Belongs to the HepT RNase toxin family.