EVOLUTIONARY HYPERVARIABILITY IN THE HINGE REGION OF THE IMMUNOGLOBULIN ALPHA-GENE

The hinge region of the immunoglobulin molecule is responsible for antigen-binding and cross-linking reactions, varying the distance between the two antigen-binding sites. As the amino acid sequence of the hinge region is identical among immunoglobulin molecules of the same (sub)class, it has been regarded as a constant region. By comparison of the nucleotide sequences among primate Cα genes, it is clear that there is a wide variety of length among the hinge regions of hominoid Cα genes, which basically consist of tandem repeats of a 15 base-pair sequence. This reiterated structure probably facilitates rapid evolutionary changes in the length of the hinge region. The hinge region of the Old World monkey Cα gene has a non-reiterated structure whose nucleotide sequence is quite different from those of the hominoid Cα genes, although its surrounding region is conserved during evolution. This unusual hypervariability reveals that the hinge region has evolved as a semi-variable region in contrast to its constant character from an ontogenic viewpoint. © 1990 Academic Press Limited.