Structural domains comprising this superfamily share the structure of the N-terminal domain of leucyl/phenylalanyl-tRNA-protein transferases (L/F-transferases), an N-end rule pathway enzyme, involved in the transfer of Leu and Phe from aminoacyl-tRNAs to exposed N-terminal Arg or Lys residues of acceptor proteins PMID:17891155. The interface of the N-terminal and C-terminal domains forms a large central cavity, where most of the conserved residues of this protein reside. The presence of this conserved residues in the central cavity of L/F-transferase suggest that this region is important for the enzyme catalysis PMID:17242373.