Sequence of the seed lectin gene from pea (Pisum sativum L.)

A pea genomic library was screened with a pea seed lectin cDNA clone, a selected clone sub-cloned and the DNA sequence determined. We have designated this gene LecA; like other lectin genes LecA contains no introns. The coding sequence of this gene is identical to that of the cDNA used to select it, pLGA.10 (1) and that of the published cDNA sequence (2). Although these cDNAa differ in their sites of polyadenylation there is only one (simple) polyadenylation signal. At the 5' end of the gene there are three in frame ATG start codons. The first of these is followed by an in frame stop codon and both the sequence surrounding thio and the third ATG are poor matches to the functional consensus (3). The second agrees well and is therefore used. Multiple start codons have been noted in lectin genes from Phaseolus vulgaris (4). LecA contains a TATA box (5) 65 bases 5' to the start codon which lies within a 22bp region duplicated between this and the start codon; such repeats also occur in Phaseolus lectin genes (4). No other consensus seqquences can be recognised in the further 5' flanking sequence and comparison with lectin genes from related species (4, 6, 7) failed to reveal regions of significant homology. When this gene was used to probe Southern blots of restriction digests of pea genomic DNA at high stringency of hybridisation, to determine the copy number of LecA, all digests gave a result indicating the presence of a single gene.