Nucleotide sequence analysis of 2″‐aminoglycoside nucleotidyl‐transferase ANT(2″) from Tn4000: its relationship with AAD(3″) and impact on Tn21 evolution

Abstract

Aminoglycoside 2″‐O‐nucleotidyltransferase (AAD(2″)) mediates bacterial resistance to dibekacin, gentamicin, kanamycin, sisomicin and tobramycin. Its coding sequence, aadB, is part of Tn21‐related transposon, Tn4000. Nucleotide sequence analysis revealed the presence of an open reading frame capable of specifying a protein of 177 amino acids with a calculated molecular weight of 21240. The predicted amino acid sequence revealed up to 27% homology to that of three nucleotidyltransferases of type AAD(3″), which are widely distributed among Gram‐negatives, and to the AAD(9) from Staphylococcus aureus transposon Tn554. The regions flanking aadB suggest that its insertion into Tn21 arose from a site‐specific recombination event adjacent to the aadA gene.