SOYBEAN GLYCININ: CHARACTERIZATION OF ITS MESSAGE AND ITS GENES
Abstract
Poly(A)-RNA was isolated from developing soybean seeds and fractionated on linear-log sucrose gradients. The major fractions sedimenting at 18S and 20S were translated in a rabbit reticulocyte lysate protein synthesis system. Immunoprecipitation using mono-specific glycinin or (beta)-conglycinin antibodies indicated that the 18S fraction directed the synthesis of glycinin precursors while the 20S fraction synthesized (beta)-conglycinin precursors. Poly(A)-RNAs enriched for glycinin coding sequences were injected into Xenopus laevis oocytes and translated in the presence of radioactive amino acids. Microsequencing was used to show that the NH(,2)-terminal leader sequences were removed from the precursors and native NH(,2)-termini of the acidic polypeptides were generated. NH(,2)-terminal sequence analysis of the glycinin precursors which still had leader sequences indicated that they contained clusters of leucine residues as observed in signal sequences of animal preproteins. Several partial genomic clones that contained coding information for glycinin subunits were characterized by nucleotide sequence analysis. In all the clones studied ((lamda)Ala, (lamda)A28-5, (lamda)A28-16 and (lamda)A28-17), the coding regions extended from midway through the acidic component to the COOH-terminus of the basic one. Clones (lamda)Ala and (lamda)A28-5 seemed to specify a member of the A(,2)B(,1a) subunit family, while (lamda)A28-16 and (lamda)A28-17 seemed to code for a member of the A(,1a)B(,2) subunit family. Nucleotide sequence analysis confirmed that glycinin genes consisted of a sequence for an acidic polypeptide component followed by that for a linker the basic polypeptide component, and some 3' flanking sequences which contained putative polyadenylation signals. The primary structures of the genes for the two subunit families were compared and their structural features were discussed.
Degree
Ph.D.
Subject Area
Biochemistry
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