We found that the structural gene for monoamine oxidase was located at 30.9 min on the Escherichia coil chromosome. Deletion analysis showed that two amine oxidase genes are located in this region. The nucleotide sequence of one of the two genes was determined. The peptide sequence of the first 40 amino acids from the N terminus of monoamine oxidase purified from E. coli agrees with that deduced from the nucleotide sequence of the gene. The leader peptide extends over 30 amino acids. The nucleotide sequence of the gene and amino acid sequence of the predicted mature enzyme (M.W. 81,295) were highly homologous to those of the maoA(K) gene and monoamine oxidase from Klebsiella aerogenes, respectively. From these results and analysis of the enzyme activity, we concluded that the gene encodes for monoamine oxidase (maoA(E)). The tyrosyl residue, which may be converted to topa quinone in the E. coil enzyme, was located by comparison with amino acid sequences at the cofactor sites in other copper/topa quinone-containing amine oxidases.