Cloning and analysis of cDNAs encoding plant storage protein precursors

Abstract

The major storage protein in many legume seeds is legumin, a hexameric molecule of molecular weight (Mr) 360,000–400,000 consisting of six subunit pairs, each of which comprises a 40,000-Mr, acidic polypeptide linked by disulphide bonds to a 20,000-Mr, basic polypeptide1. We have recently shown that these subunit pairs are synthesized, in vivo and in vitro in Pisumand Vicia2,3, as a 60,000-Mr precursor polypeptide, putatively containing one copy each of the acidic and basic summits covalently linked together. We describe here the cloning and identification of cDNA sequences coding for the legumin precursor. Additionally, we have used these cDNAs to verify that the legumin mRNAs are of sufficient size to code for the precursor and to demonstrate the presence of four single-copy legumin genes in genomic DNA. Possible mechanisms for the processing of the legumin precursor are discussed. Identification of cloned cDNA sequences coding for vicilin, the secondary storage protein of Pisum sativum4, is also reported.