Characterization of a bean (Phaseolus vulgaris L.) malic-enzyme gene

We have isolated a genomic clone encoding a plant NADP(+)-dependent malic enzyme (NADP-ME). This clone, isolated from bean (Phaseolus vulgaris L.), covers the entire gene (exons, introns) and 5'-flanking regions. DNA sequencing defines 20 exons spanning approximately 4.5 kb, which range over 48-235 bp in size. All 19 introns are fairly small (79-391). The first intron resides in the 5'-untranslated leader sequence. Introns 10, 11 and 16 are located at positions identical to a rat malic-enzyme gene. In the promoter region, a TATA box (TATATATA) is easily recognized 41 bp upstream of a single transcription-initiation site. Two potential cis-acting elements with homology to elements from plant genes, activated by UV light and fungal elicitors, were identified at positions -153 and -312, respectively. Southern-blot analysis suggests a single gene copy, but also other distantly related genes, in the bean genome. The deduced NADP-ME protein of 589 amino acids exhibits features consistent with a cytoplasmic location. We describe the organization of the NADP-ME protein into functional domains located on separate exons. The evolution of malic-enzyme genes coding for isoforms in different cellular compartments of plants and animals is discussed.