A NOVEL ANTHER-EXPRESSED ADH-HOMOLOGOUS GENE IN LYCOPERSICON-ESCULENTUM

Two novel tandemly-oriented open reading frames (ORFs) with homology t o alcohol dehydrogenase (ADH) were isolated from tomato. The predicted amino acid composition for each of the two tandem adh genes indicates the presence of 22 and 21, respectively, of 22 amino acids conserved in ADH proteins from plants and animals. However, comparison to known plant adh genes reveals a significantly lower similarity indicating th at they belong to a novel class of ADHs. According to mapping data, th e adh-homologous ORFs do not represent either of the previously studie d adh1 or adh2 genes of tomato. The tandem genes, termed adh3a and adh 3b, mapped to a distal region of the long arm of chromosome 4, unlike adh1, which maps closer to the centromere. Adh3a and adh3b have over 9 0% similarity to each other at the nucleotide and putative peptide lev els. The adh3a gene has ten exons and nine introns with the transcript ion initiation site 57 bp upstream of the translation start. A putativ e TATA box and polyadenylation site have been identified. Adh3a is tra nscribed and, according to cDNA sequence analysis, fully processed in the late stages of anther development. According to transformation ana lysis, tissue-specific regulatory elements reside within the -448 to 724 region. The termination codon of adh3a is separated from the putat ive adh3b translation start site by 789 bp of intervening sequence. Th e 5' untranscribed sequences of each gene contain a stretch of 68 bp w ith 78% similarity. Within this stretch are sequences which are homolo gous to sequences found in anaerobically-induced or pollen-expressed g enes from various plant species.