The IA and IE products of B10.S(9R), B10.A, B10.KPB128, and B10.GAA37 were analyzed for primary structural variations by comparative tryptic peptide mapping. The Aα, Aβ, and Eβ products of B10.S(9R) and B10.A differed in about 40% of their acid-soluble tryptic peptides, indicating that intra-I-region recombinant strain B10.S(9R) received the genes encoding Aα, Aβ, and Eβ from the H- 2s parental chromosome rather than from H- 2a. The tryptic peptides of Eα chains from B10.S(9R) and B10.A were indistinguishable, suggesting that B10.S(9R) received the gene encoding the Eα chain from the H- 2a parental chromosome. Consistent with the results of others, these data suggest that the genes encoding Aα, Aβ and Eβ chains are centromeric to the IJ subregion, while the gene encoding Eβ chains is telomeric to IJ. The I-region products of two congenic lines carrying wild-derived H- 2 haplotypes on a C57BL/10 background, designated B10.KPB128 and B10.GAA37, are serologically indistinguishable from those of B10.S(9R). The IA and IE products of B10.S(9R) were compared with those of B10.GAA37 and B10.KPB128 to determine the structural similarity of serologically identical products from allopatric populations of wild mice. The Aα, Aβ, and Eβ products of B10.S(9R) were indistinguishable from those of B10.GAA37 and B10.KPB128 by comparative tryptic peptide mapping. The Eα chains of these three lines differed in one or two of their acid-soluble tryptic peptides. The results indicate that the IA-encoded products of these three lines are structurally very similar and may be identical suggesting that some alleles of the Aα, Aβ, and Eβ chains may be maintained in stable linkage associations in allopatric populations of wild mice. The minor structural variations detected in the Eα chains of these three congenic lines indicate that the Eα chain is encoded by chromosome 17 and suggest that allelic Eα chains exhibit considerably less structural variability than other I-region encoded antigens.
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