The nucleotide (nt) sequence of the genes encoding the oxidation of aniline and o-toluidine to the corresponding catechols was determined in the Acinetobacter sp. strain YAA. The 6293-bp DNA region sequenced contained five genes (atdA1-A5) in one strand. From the deduced amino acid (aa) sequences, the atdA1-A5 genes were predicted to encode a glutamine synthetase-like protein (AtdA1), a glutamine amidotransferase-like protein (AtdA2) and three subunits of benzene-ring hydroxylating oxygenase [the large and small subunits of the terminal dioxygenase component (AtdA3 and AtdA4) and the reductase component (AtdA5)] in this order. A glutamine synthetase ATP-binding motif and a putative glutamine amidotransferase class-I active site were found in AtdA1 and AtdA2, respectively, whereas Rieske-type-and plant ferredoxin-type-[2Fe-2S] binding motifs were found in AtdA3 and AtdA5, respectively. These results suggest that, in aniline oxidation in this strain, the former two gene products (AtdA1 and AtdA2) are involved in the recognition and release of aniline amino-groups, while the latter three (AtdA3, AtdA4 and AtdA5) are involved in dihydroxylation of the benzene-ring. Although this aniline oxidation system has a significant resemblance (31.1-62.0% homology at the aa sequence level) to that from Pseudomonas putida UCC22 (Fukumori and Saint, J. Bacteriol., 179, 399-408, 1997), the G+C content of these Acinetobacter genes (40.1-47.4%) is quite different from that of the Pseudomonas genes, tdnQTA1A2B (63.1-71.2%). Polypeptide analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis confirmed the production of all the above polypeptides with a molecular mass calculated from each aa sequence.