<jats:p>The DNA sequence of an aminoglycoside phosphotransferase gene (aph) from Streptomyces fradiae ATCC 10745 (a neomycin producer) was determined. The gene was localized by in vitro subcloning and insertional inactivation. Molecular weight, amino acid composition, and amino-terminal analysis of the purified aph gene product confirmed the accuracy and position of the aph gene sequence. Pairwise comparisons of S. fradiae aph with the aph genes encoded by bacterial transposons Tn5 and Tn903 showed significant nucleotide and amino acid homologies which indicated a common evolutionary origin for these antibiotic-resistance genes.