Identification of a diversity segment of human T-cell receptor beta-chain, and comparison with the analogous murine element.

The humoral immune system antigen-binding proteins (immunoglobulins) are disulphide-linked heterodimers of light and heavy chains. The gene for the variable region which determines antigen specificity is assembled when one member from each of the dispersed clusters of variable (V) gene segments, diversity (D) elements (for the heavy chains only) and joining (J) segments rearrange and fuse during B-cell development (reviewed in ref. 1). Short recognition sequences adjacent to these elements appear to be involved in the recombination process. The cellular immune system antigen recognition proteins are receptors on the surface of T cells, which are composed of disulphide-linked alpha-chains and beta-chains, each of which has a variable and constant region. Recently, cDNA clones of the beta-chain mRNA have been isolated; the genomic arrangement is very similar to immunoglobulin genes with multiple V beta genes, and two clusters of J beta segments, each of which is upstream from a constant-region gene segment. The V beta and J beta segments have adjacent recombinational recognition sequences like the immunoglobulin elements. However, approximately 10 nucleotides of the cDNA clones between the V beta and J beta regions were not present in the corresponding genomic elements and may have been due to intervening D beta segments. Here we describe a diversity element (D beta 1.1) in a region of high human-mouse homology about 650 bases 5' to the first J beta cluster. Two transcripts which include sequences upstream of D beta 1.1 are found in the human thymus. This region may have some other function besides providing the beta-chain with a diversity segment.