POLYMORPHISM OF LEGUMIN SUBUNITS FROM FIELD BEAN (VICIA-FABA L VAR MINOR) AND ITS RELATION TO THE CORRESPONDING MULTIGENE FAMILY

Legumin, which amounts to approximately 55% of the seed protein in fie ld beans (Vicia faba L. var. minor), is a representative of the 12S st orage globulin family. The 12S storage globulins are hexameric holopro tein molecules composed of different types of polymorphic subunits enc oded by a multigene family. 'Type-A' legumin subunits contain methioni ne whereas type-B' are methionine-free subunits. Sequencing of two dif ferent type A-specific cDNAs, as well as an FPLC/HPLC-based improvemen t of subunit fractionation and peptide mapping with subsequent partial amino-acid sequencing, permit the assignment of some of the polymorph ic legumin subunits to members of the multigene family. Two different type A subunits (A1 and A2) correspond to the two different cDNA clone s pVfLa129 (A2) and 165 (A1), but microheterogeneity in the amino-acid sequences indicates that polymorphic variants of both representatives of this type may exist. Two groups of published type B-specific gene sequences (LeB7, and LeB2, LeB4, LeB6, respectively) are represented b y two polymorphic subunit fractions (B3I, B3II, and B4I, B4II). A seve nth clone, LeB3, encodes one of the large legumin subunits that is onl y a minor component of the legumin seed protein complex.