Pseudomonas iodinum IFO 3558 adenosine deaminase(ADA) gene was cloned by the polymerase chain reaction and deduced the amino acid sequence of the enzyme. DNA sequence homology of Pseudomonas iodinum IFO 3558 ADA gene was compared to those of E. coli, human and mouse ADA genes. Unambiguous sequence from both strands of pM21 was obtained for the region believed to encode ADA. The sequence included a 804-nucleotide open reading frame, bounded on one end by sense primer and on the other end by two antisense primer. This open reading frame encodes a protein of 268 amino acids having a molecular weight of 29,448. The deduced amino acid sequence shows considerable similarity to those of E. coli, mouse and human ADA. Pseudomonas iodinum IFO 3558 nucleotide sequence shows 98.5% homology with that of the E. coli ADA sequence and 51.7% homology with that of the mouse ADA sequence and 52.5% homology with that of the human ADA sequence. The ADA protein sequence of Pseudomonas iodinum IFO 3558 shows 96.9% homology with that of the E. coli and 40.7% homology with that of the mouse and 41.8% homology with that of the human. The distance between two of the conserved elements, TVHAGE and SL(1)NTDDP has veen exactly conserved at 76 amino acids for all four ADAs. Two of the four conserved sequence elements shared among the four ADAs are also present in the yeast, rat, human (M), and Human(L) AMP deaminase. The SLSTDDP sequence differs only in the conservative substitution of a serine for an asparagine. A conserved cysteine with conserved spacing between these two regions is also found. Thus, sequence analysis of four ADAs and four AMP deaminases revealed the presence of a highly conserved sequence motif, SLN(S)TDDP, a conserved dipeptide, HA, and a conserved cysteine residue.