Cloning and sequence analysis of the human major histocompatibility complex gene DC-3 beta

The DC antigen is one of the class II major histocompatibility antigens involved in the regulation of the immune response. This molecule is a heterodimer composed of an alpha and a beta chain. Southern blot analysis of several homozygous cell lines shows that there are two DC beta genes. The DC-3 beta gene, corresponding to a polymorphic restriction fragment, was cloned and sequenced and found to exist in five exons spanning 8 kilobase pairs of DNA. These exons correspond to the functional domains of the DC beta protein. Comparison of the beta 1 domains of known DC beta chains shows that the polymorphism is clustered in four regions. A similar comparison of the mouse A beta sequences shows only two prominent diversity regions. The DC beta chain sequences are eight amino acids shorter than the A beta chain sequences due to the elimination of a small exon by an aberrant splice acceptor.