Storage protein precursor polypeptides in cotyledons of Pisum sativum L.. Identification of, and isolation of a cDNA clone for, an 80000-Mr legumin-related polypeptide

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Abstract
An 80,000-MW polypeptide, which bound to anti-legumin IgG, was detected among labeled polypeptides from cotyledons at late stages of development. When poly(A)-containing RNA from similar cotyledons was translated in a cell-free protein-synthesized system, an 80,000-MW polypeptide was also detected. Immunoprecipitation of translation products with anti-legumin IgG showed that, in addition to the major legumin precursor polypeptides of MW approximately 60,000, the 80,000-MW polypeptide was specifically immunoprecipitated. A c[complementary]DNA clone pCD32, was found to select an RNA coding for an 80,000-MW polypeptide in hybrid-selection experiments. Additional minior polypeptides of MW 63,000 and 65,000 were present in translocation products of RNA selected by pCD32; all 3 polypeptides were immunoprecipitated by anti-legumin IgG. Thermal elution of RNA bound to pCD32 showed that the affinity of pCD32 to the RNA coding for the 80,000-MW polypeptide was greater than to the RNA coding for the 63,000-MW and 65,000-MW polypeptides. In similar hybrid-selection experiments, another cDNA clone, pCD40, selected RNA coding predominantly for polypeptides of MW 63,000 and 65,000. A minor polypeptide of MW 80,000 was also detected among these products; again all 3 polypeptides were immunoprecipitated by anti-legumin IgG. Peptide mapping revealed close similarities between the 80,000-MW polypeptide and the 63,000-MW/65,000-MW polypeptides obtained by translation of RNA selected by pCD32. There were also similarities between maps obtained from translation products of RNA selected by pCD32 and those obtained from anti-legumin IgG immunoprecipitates of total translation products of poly(A)-containing RNA.