The glycosylated seed storage proteins of Glycine max and Phaseolus vulgaris. Structural homologies of genes and proteins

Considerable information is now available concerning the 7 S seed storage proteins of legumes and the genes that encode them. Our study compares the gene encoding a β-type subunit of phaseolin (Pvu β), the 7 S protein of common bean (Phaseolus vulgaris), with the gene encoding an α'-subunit of β-conglycinin (Gma α'), the 7 S protein of soybean (Glycine max). The comparison involves 2880 base pairs of Pvu β and 3636 base pairs of Gma α' and includes approximately 1 kilobase pair of 5'-flanking sequences, and 5' and 3' untranslated sequences, as well as the six exons and five introns that are found to occur in similar positions in both genes. Conserved sequences in the 5'-flanking regions of these genes are discussed in light of their potential regulatory role. Published sequences for 7 S genes of pea (Pisum sativum) permit the interference of the nature and direction of evolutionary change and, in particular, show that the major size difference between the large Gma α' polypeptide and the smaller polypeptides of pea and common bean is due to a large insertion in the first exon of Gma α'. Comparisons of protein primary structure, potential glycosylation sites, and predicted protein hydropathy show that strongly conserved features of 7 S proteins cut across exon boundaries and that nonconserved regions exist that may have potential for protein modification.