Structure-function analyses for aminoglycoside 3'-phosphotransferase II (APH(3')-II).

Mutant strains containing APH(3')-II were constructed via site-directed mutagenesis of the cloned gene and by random mutagenesis of a strain containing the APH(3')-II gene on a conjugative plasmid. Substitutions at highly conserved amino acid residues produced APH(3') enzymes which in general showed reduced activity and conferred reduced levels of resistance to their substrates. Substitutions at Tyr 218 altered substrate specificity for the enzymes. Random mutagenesis produced plasmid-borne mutations conferring amikacin resistance. Two of these mutations appeared to be localized to the APH(3')-II structural gene.