Antitoxin component of a type II toxin-antitoxin (TA) system. Antitoxin that directly inhibits activity of EndoA in vitro. Upon expression in E.coli counteracts inhibitory effect of endoribonuclease EndoA. The EndoA-EndoAI complex does not seem to bind its own promoter (PubMed:24120662). Homodimer, forms a heterohexamer composed of alternating toxin and antitoxin homodimers which inhibits the toxin's endoribonuclease activity. Antitoxin prevents RNA binding to the endoribonuclease (PubMed:24120662). Belongs to the MazE/EndoAI family.