GENOMIC STRUCTURE AND EXPRESSION OF THE ADH7 GENE ENCODING HUMAN CLASS-IV ALCOHOL-DEHYDROGENASE, THE FORM MOST EFFICIENT FOR RETINOL METABOLISM IN-VITRO

Human alcohol dehydrogenase (ADH) consists of a family of five evoluti onarily related classes of enzymes that collectively function in the m etabolism of a wide variety of alcohols including ethanol and retinol, Class TV ADH has been found to be the most active as a retinol dehydr ogenase, thus it may participate in retinoic acid synthesis, The gene encoding class IV ADH (ADH7) has now been cloned and subjected to mole cular examination, Southern blot analysis indicated that class TV ADH is encoded by a single unique gene and has no related pseudogenes. The class TV ADH gene is divided into nine exons, consistent with the hig hly conserved intron/exon structure of other mammalian ADH genes, The predicted amino acid sequence of the exon coding regions indicates tha t a protein of 373 amino acids, excluding the amino-terminal methionin e, would be translated, sharing greater sequence identity with class I ADH (69%) than with classes II, III, or V (59-61%), Expression of cla ss Pr ADH mRNA was detected in human stomach but not liver, This corre lates with previous protein studies, which have indicated that class I V ADH is the major stomach ADH but unlike other ADHs is absent from li ver, Primer extension studies using human stomach RNA were performed t o identify the transcription initiation site lying 100 base pairs upst ream of the ATG translation start codon. Nucleotide sequence analysis of the promoter region indicated the absence of a TATA box sequence of ten located about 25 base pairs upstream of the start site as well as the absence of GC boxes, which are quite often seen in promoters lacki ng a TATA box. The class TV ADH promoter thus differs from the other A DH promoters, which contain either a TATA box (classes I and II) or CC -boxes (class III), suggesting a fundamentally different form of trans criptional regulation.