The APH gene of a butirosin-producing Bacillus circulans was cloned and shown to be expressed in Escherichia coli and Streptomyces lividans. The gene was sequenced and a possible developmentally regulated promoter identified. When the deduced protein sequence was compared with those from transposon Tn5, transposon Tn903, Streptomyces fradiae, Staphylococcus aureus and Streptococcus faecalis, significant homology was found, indicating that the genes may have a common origin.