A 28-KILODALTON POD STORAGE PROTEIN OF FRENCH BEAN-PLANTS - PURIFICATION, CHARACTERIZATION, AND PRIMARY STRUCTURE

When French bean (Phaseolos vulgaris) plants were depodded in the earl y stages of fruit development, relative levels of a specific protein w ith a relative molecular weight of 28,000 were enhanced in the young p ods that formed later. The protein, designated pod storage protein (PS P), was purified from extracts of newly formed pods from plants that h ad been previously depodded four times at intervals of 2 weeks. Two-di mensional polyacrylamide gel electrophoresis showed the presence of th ree forms (designated A, B, and C) of PSP with identical electrophoret ic mobilities but different charges. The molecular mass of native PSP was estimated by gel filtration to be 67 kD; therefore, the protein wa s most likely present as a dimer. The antisera raised against forms A and C were crossreactive with each other. Form B lacked the N-terminal alanine of forms A and C. An expression library from French bean pods was screened using the antiserum against form A, and a full-length cD NA clone was isolated. The cDNA insert included 765 bp potentially enc oding a polypeptide with 255 amino acid residues (and a calculated mol ecular mass of 28,854 D). The amino acid sequence deduced from the PSP cDNA had 65 to 71% identity with soybean (Glycine max) vegetative sto rage protein sequences (P.E. Staswick [1988] Plant Physiol 87: 250-254 ; and Correction [1989] Plant Physiol 89: 717). Genomic Southern blot analysis suggested that PSP is derived from a single-copy gene.