Structure and Expression of Genes Encoding the Soybean 7S Seed Storage Proteins
The 7S seed storage proteins (vicilins) of soybean (Glycine max) are trimeric holoproteins that accumulate during the cotyledon and maturation stages of seed development. The α’, α and β subunits represent the majority of the subunits. To a lesser degree another group of subunits (the γ subunits) are also found in the vicilin proteins. The synthesis of each of these subunits is differentially regulated. Several of the messenger RNAs (mRNAs) encoding these subunits contain identical nucleotide sequences, but also unique sequences specific for the individual subunits.
The nucleotide sequence of a gene encoding an α’ subunit of soybean vicilin was compared with the published partial sequence of a gene encoding a subunit of the vicilin protein of Phaseolus vulgaris (Sun et al., 1981). The overall structure of the genes and the predicted secondary structures of the subunits were similar. The differences in the lengths of the mRNAs that encode the two subunits result, at least in part, from a number of nucleotide deletions and duplications that have occurred in their respective genes.
The two major storage proteins of soybeans (Glycine max) which have sedimentation coefficients of 7S and 11S are referred to as the vicilins and legumins, respectively. The research in our laboratory deals primarily with the vicilin proteins. In this paper we present a summary of the information that has accumulated on these proteins. Our discussion will focus on (1) the biosynthesis of the soybean vicilins, (2) the differential accumulation of vicilin subunits, (3) the structure of the messenger RNAs and genes that encode some of the vicilin subunits, and (4) a comparison of a soybean vicilin subunit with a subunit of Phaseolus vulgaris vicilin. By a combination of such research approaches we hope to better understand the structure and function of the soybean vicilins.
KeywordsStorage Protein Amino Acid Difference Cyanogen Bromide Primary Amino Acid Sequence Storage Protein Gene
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