Detailed sequence analysis suggests that members of this family represent the minimal domain of the PolB nucleotidyltransferase superfamily []. The conservation of the nucleotidyltransferase core and particularly the negatively charged metal-chelating residues lead to the prediction that members of this family possess nucleotidyltransferase activity. Their small size, however, leaves very little beyond the core catalytic domain to help in specific substrate recognition as seen in other, larger members of the PolB superfamily []. The conserved region of the MNTs ("minimal"nucleotidyltransferases) includes approximately 90 amino acid residues that correspond to the core domain of kanamycin nucleotidyltransferase []. A structural model of the MNT domain has been proposed [].
