CHARACTERIZATION OF A BEAN (PHASEOLUS-VULGARIS L) MALIC-ENZYME GENE

We have isolated a genomic clone encoding a plant NADP(+)-dependent ma lic enzyme (NADP-ME). This clone, isolated from bean (Phaseolus vulgar is L.), covers the entire gene (exons, introns) and 5'-flanking region s. DNA sequencing defines 20 exons spanning approximately 4.5 kb, whic h range over 48-235 bp in size. All 19 introns are fairly small (79-39 1 bp). The first intron resides in the 5'-untranslated leader sequence . Introns 10, 11 and 16 are located at positions identical to a rat ma lic-enzyme gene. In the promoter region, a TATA box (TATATATA) is easi ly recognized 41 bp upstream of a single transcription-initiation site . Two potential cis-acting elements with homology to elements from pla nt genes, activated by UV light and fungal elicitors, were identified at positions -153 and -312, respectively. Southern-blot analysis sugge sts 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 organ ization of the NADP-ME protein into functional domains located on sepa rate exons. The evolution of malic-enzyme genes coding for isoforms in different cellular compartments of plants and animals is discussed.