Structural studies on the murine Ia alloantigens. IV. NH2-terminal sequence analysis of allelic products of the I-A and I-E/C subregions.

Murine Ia alloantigens encoded by the I-A and I-E/C subregions were isolated from radiolabeled splenic lysates and examined by NH2-terminal sequence analysis. Haplotype-associated sequence variation was detected in the beta, but not alpha, subunits of both the A and E/C alloantigens. The A beta-polypeptides from k and b haplotypes show four differences in the 12 positions compared, whereas the E/C beta-polypeptides from k and r haplotypes show two differences in the 13 positions compared. No sequence variation was detected between the Ak and Ab alpha-chains (six positions compared) or between the E/Ck and E/Cr alpha-chains (11 positions compared). Homology relationships between these murine Ia alloantigens and the human Ia (DR) alloantigens are also presented.