Structure of the murine immune response I-A β locus: Sequence of the I-A β gene and an adjacent β-chain second domain exon

The murine major histocompatibility complex I region encodes two class II antigens, I-A and I-E. From a mouse spleen DNA cosmid library of the b haplotype, we isolated a clone containing the entire I-A β gene and a separate exon encoding a β-chain second domain (A β2). The A β gene, encompassing more than 6 kb, is encoded by six exons corresponding to the different domains of the A β polypeptide. The translated A β amino acid sequence displays 73% homology to human DC β chains; homologies to other subsets of human β-chains are lower, establishing that I-A corresponds structurally to DC. The A β2 exon is about 20 kb centromeric to the A β gene. Its translated amino acid sequence includes all the conserved amino acids of other class II β-chain second domains. It shows about 60% homology to each of three subsets of human β-chains available for comparison, and to the A β chain. No A β2 first domain exon has been detected with A β or DC β probes.