Characteristics of two types of legumin genes in the field bean (Vicia faba L.var. minor) genome as revealed by cDNA analysis

Nucleotide sequence analysis of cDNA clones coding for field bean legumin precursor polypeptides revealed two different types, called A and B. Although homologous, both types differ in several sequence characteristics. Comparison with similar data from soybean and recent findings from pea leads to the following conclusions: (i) the two types of legumin genes described represent two subfamilies, A and B, which are probably of widespread occurrence; (ii) legumin genes or subunits can best be placed in either subfamily A or B by sequence homology, in addition B‐type subunits contain generally fewer (or none at all in V. faba) Met residues as compared to A‐type subunits; (iii) members of one subfamily from different species are more homologous than members of either subfamily within a species, therefore the two subfamilies must have arisen long before speciation of the genera Glycine, Pisum and Vicia; (iv) during speciation members of the B‐subfamily diverged significantly more than members of the A‐subfamily.