title: Evolutionary relationship between HLA-DR antigen beta-chains, HLA-A, B, C antigen subunits and immunoglobulin chains.
abstract: cDNA for a beta-chain of HLA-DR antigens was cloned and the partial nucleotide sequence was determined. The data suggest that the beta-chain consists of approximately 230 amino acids, of which about 200 are exposed on the cell surface. The beta-chain appears to be composed of two exposed disulphide-containing domains. The arrangement of the disulphide loops suggests that the beta-chain is similar in structure to the HLA-A, B, C antigen subunits and the immunoglobulin chains. For the beta-chain domain closest to the membrane this similarity was verified at the level of primary structure. The partial amino acid sequence of the NH2-terminal domain did not display any apparent homology to HLA-A, B, C antigens and immunoglobulins. However, the similarity established here between the two types of major histocompatibility antigen subunits and the immunoglobulin chains suggests a common ancestral origin for at least some regions of these molecules.
mesh_terms: D001483:Base Sequence; D005075:Biological Evolution; D003001:Cloning, Molecular; D004247:DNA / Q000032:analysis*; D006680:HLA Antigens / Q000235:genetics*; D000949:Histocompatibility Antigens Class II / Q000235:genetics*; D006801:Humans; D007136:Immunoglobulins / Q000235:genetics*; D011498:Protein Precursors / Q000235:genetics*
chemical_list: D006680:HLA Antigens; D000949:Histocompatibility Antigens Class II; D007136:Immunoglobulins; D011498:Protein Precursors; D004247:DNA