The aspartate aminotransferase-P2 gene from Lupinus angustifolius.

and plays a key role in carbon and nitrogen metabolism in plants. The enzyme has been shown to be involved in the shuttling of reducing equivalents from the cytoplasm to chloroplasts, mitochondria, glyoxysomes, and peroxisomes via the malate-aspartate shuttle (Wightman and Forest, 1978). Up to five separate isoforms of AAT have been reported in plants, differing both kinetically and in levels and place of expression (Wightman and Forest, 1978). In the nitrogenfixing root nodules of lupin (Lupinus angustifolius), two isoforms of AAT, AAT-Pl and AAT-P2, have been described and were found to differ in their kinetic properties and expression characteristics throughout nodule development (Reynolds and Famden, 1979). AAT-P2 from L. angustifolius has been shown to be expressed in an inducible manner concomitantly with the onset of biological nitrogen fixation (Reynolds and Famden, 1979) and to be localized in the nodule proplastid (Boland et al., 1982), whereas the AAT-P1 isoform is localized in the cytoplasm and appears to be constitutively expressed. Similar results have been obtained for the AAT isoforms present in alfalfa nodules (Farnham et al., 1990; Robinson et ai., 1994). The cDNAs encoding the lupin isoforms have been obtained (Reynolds et al., 1992; Winefield et al., 1994). Legume AAT cDNAs have also been cloned recently from Medicago sativa (Udvardi and Kahn, 1991; Gantt et al., 1992). To our knowledge this work is the fmt report of a genomic sequence for the plastid-localized plant AAT-P2 isoform The 6.9 kb of DNA sequenced contains a 1785-bp 5’ flanking sequence, 11 exons, 10 introns, and 1229 bp of 3‘ sequence (Table I). Intron-exon borders were mapped by comparison with the L. angustifolius cDNA sequence (Reynolds et al., 1992). A consensus TATA motif was observed 68 bp 5‘ of the initiating ATG. A consensus poly(A) addition signal was observed 259 bp 3’ of the translation stop codon. This is in agreement with the observed polyadenylation of the mRNA (Reynolds et al., 1992). Genomic southem hybridization data were consistent with a single copy of the AATP I gene in the L. angustifolius genome.