Structural studies on the murine ia alloantigens-III. Tryptic peptide comparisons of allelic products of the I-E/C sub-region

Splenocytes from B10 congenic mice of the k, p, d, and r haplotypes were radiolabeled with ³H- or ¹⁴C-arginine, lysine, leucine and tyrosine. The E/C sub-region products were precipitated from NP40 lysates with specific alloantisera and the la α and β sub-units of each of the above four haplotypes were isolated by gel electrophoresis. Molecules to be compared, one ³H-labeled and the other ¹⁴C-labeled, were mixed, digested with trypsin, and the acid soluble peptides analyzed by ion-exchange chromatography. The results indicate that the α sub-units of p, d and r are approximately 90% homologous to k. In contrast, β polypeptides of the above three haplotypes have only about 50% coincidence of peptides with the k allelic product. This degree of structural variation suggests that the β sub-unit of the E/C product is encoded by the major histocompatibility complex.