Three human alcohol dehydrogenase subunits: cDNA structure and molecular and evolutionary divergence.

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Abstract
Class I human alcohol dehydrogenase (ADH; alcohol:NAD+ oxidoreductase, EC 1.1.1.1) consists of several homo- and heterodimers of .alpha., .beta. and .gamma. subunits that are governed by the ADH1, ADH2, and ADH3 loci. We previously cloned a full length of cDNA for the .beta. subunit, and the complete sequence of 374 amino acid residues was established. cDNAs for the .alpha. and .gamma. subunits were cloned and characterized. A human liver cDNA library, constructed in phage .lambda.gt11, was screened by using a synthetic oligonucleotide probe that was matched to the .gamma. but not to the .beta. sequence. Clone pUCADH.gamma.21 and clone pUCADH.alpha.15L differed from .beta. cDNA with respect to restriction sites and hybridization with the nucleotide probe. Clone pUCADH.gamma.21 contained an insertion of 1.5 kilobase pairs (kbp) and encodes 374 amino acid residues compatible with the reported amino acid sequence of the .gamma. subunit. Clone pUCADH.alpha.15L contained an insertion of 2.4 kbp and included nucleotide sequences that encode 374 amino acid residues for another subunit, the .alpha. subunit. In addition, this clone contained the sequences that encode the COOH-terminal part of the .beta. subunit at its extended 5'' region. The amino acid sequences and coding regions of the cDNAs of the three subunits are very similar (.apprxeq. 93-95% identity). A high degree of resemblance is observed also in their 3'' noncoding regions. However, distinctive differences exist in the vicinity of the Zn-binding cysteine residue at position 46-i.e., Cys-Gly-Thr in the .alpha., Cys-Arg-Thr in the wild-type .beta.1, Cys-His-Thr in the Oriental-type .beta.2, and Cys-Arg-Ser in the .gamma., reflecting the differences in their kinetic properties. Based on the cDNA sequences and the deduced amino acid sequences of the three subunits, their structural and evolutionary relationships are discussed.