Multiple sequences related to classical histocompatibility antigens in the mouse genome

A series of genes on the 17th chromosome of the mouse, called the major histocompatibility complex, has critical roles in the immune response. The classical transplantation antigens (or H-2 antigens) are encoded by genes located in several loci of this complex - H-2K, H-2D and H-2L (refs 1, 2; Fig. 1). The antigens are cell-surface glycoproteins consisting of a single polypeptide chain of about 350 amino acids, non-covalently associated to a shorter polypeptide chain, β2-microglobulin, which is not encoded by the 17th chromosome. Within a given H-2 haplotype, H-2K, -D or -L antigens differ by discrete antigenic sites, probably due to changes in their amino acid sequences³. As many as 50 alleles have been found for each K and D locus in the laboratory mouse; thus H-2 loci are very polymorphic². We report here a preliminary study of the structure of H-2 genes, in which the number of H-2-related sequences in the mouse genome has been estimated from the number of DNA fragments able to hybridize specifically with a cDNA carrying an H-2 sequence.