Toxic component of a type II toxin-antitoxin (TA) system. Upon expression in M.smegmatis inhibits colony formation. Its toxic effect is neutralized by coexpression with cognate antitoxin MazE5 (PubMed:20011113). Probably an endoribonuclease (By similarity). Forms a complex with cognate antitoxin MazE5. Repressed by Mce3R. Belongs to the PemK/MazF family.