A variant alpha-chain in an Ia molecule from the I-A subregion of the mouse major histocompatibility complex: a possible intragenic recombination.

The recombinant MHC haplotype t1, present in mouse strain A.TL and B10.TL, encodes an I-A molecule with a variant alpha-chain that was recognized when tryptic peptide digests from t1 and the nominal parental haplotype (a1 or k) were compared by double-label reverse phase HPLC. The t1 I-A alpha-chain possesses a tryptic peptide absent from a1 and k I-A alpha-chains, and lacks several peptides present in a1 and k. The peptide that differs in t1 is not a mannose-bearing peptide, and thus its altered mobility is probably not due to carbohydrate modification. The alteration in t1 could result from mutation or intragenic recombination, but the unique t1 peptide migrates in a position identical to a peptide found in haplotype s, a partner in the (s X a1) cross that generated the t1 recombinant. If this apparently shared peptide indicates an intragenic recombination, this places the I-A alpha-gene centromeric to the other I-A subregion gene, and together with the data of Jones, suggests a gene order of I-A alpha, I-A beta, I-E beta (A alpha, A beta, Ae).