A rice glutelin and a soybean glycinin have evolved from a common ancestral gene

A cDNA clone covering the entire coding region for a glutelin subunit precursor has been identified from a library of endosperm-developing rice cDNA clones using a mixed oligodeoxynucleotide probe, and then by immunoprecipitation of hybrid-selected translation product with an antiserum against the acidic polypeptides of the glutelin. Analysis of the cDNA insert revealed that rice glutelin is synthesized as precursor polypeptides which undergo post-translational processing to form the nonrandom polypeptide pairs, like glycinin precursors of soybean. By comparing the predicted protein sequence of this precursor from monocots with that of glycinin A1aB1b precursor from dicots, it was found that the overall 32% of the amino acid positions are identical in both proteins. Because regions which show identities are dispersed throughout both molecules, the similarity is not due to convergent evolution, but to divergence evolution from a common ancestral gene.