Human stomach aldehyde dehydrogenase cDNA and genomic cloning, primary structure, and expression in Escherichia coli.

An aldehyde dehydrogenase isozyme, ALDH3, which is strongly expressed in the stomach, may play a role in the oxidation of toxic aldehydes. Using reverse genetic approach, we cloned and characterized the cDNA and the gene for the ALDH3. The full length cDNA is 1624 base pairs (bp) in length and contains an open reading frame encoding 453 amino acid residues. The deduced amino acid sequence shows a high degree of resemblance to that of rat hepatocarcinoma ALDH. The human ALDH3 gene spans about 8 kb in length and consists of 10 exons. The putative TATA and CCAAT boxes are located in the consensus upstream distance from the transcription initiation site. Southern blot analysis of total genomic DNA argues against the proposed two-gene model for the ALDH3 isozymes (Yin, S.-J., Cheng, T.-C., Chang, C.-P., Chen, Y.-J., Chao, Y.-C., Tang, H.-S., Chang, T.-M., and Wu, C.-W. (1988) Biochem. Genet. 26, 343-360). Northern blot hybridization and analysis of PCR amplification products of cellular RNA demonstrated the existence of a high level of ALDH3 mRNA in human stomach and hepatoma cells, but a very low level in the normal liver. Expression of ALDH3 cDNA in Escherichia coli yielded a protein of 55 kDa, which exhibited kinetic properties similar to that found in ALDH3 isozyme purified from human stomach and liver, and was hybridizable with rabbit anti-human-hepatoma ALDH serum.