Exhibits a very high intrinsic GTPase hydrolysis rate. Involved in the addition of a carboxymethylaminomethyl (cmnm) group at the wobble position (U34) of certain tRNAs, forming tRNA-cmnm(5)s(2)U34. Binds 1 potassium ion per subunit. Homodimer. Heterotetramer of two MnmE and two MnmG subunits. No visible phenotype. Belongs to the TRAFAC class TrmE-Era-EngA-EngB-Septin-like GTPase superfamily. TrmE GTPase family.