Evidence for two homologous, but nonidentical, Ia molecules determined by the I-EC subregion

Sequential immunoprecipitation, two-dimensional gel electrophoresis and peptide mapping analyses of B10A(3R), 35S-methionine-labeled, I-EC subregion products were performed. Evidence is presented here for the presence of two structurally homologous, but nonidentical, gene products of the I-EC subregion. These two Ia molecules are independently immunoprecipitable, identical in molecular size and charge, but differ by approximately equal to 20% in their peptides obtained by partial digestion with Staphylococcus aureus protease V8.