The human T cell receptor alpha-delta locus: a physical map of the variable, joining and constant region genes.

In this study a physical macro-restriction map of the entire human alpha locus that spans about 1000 kilobase pairs and includes the V alpha, J alpha and C alpha genes is presented. Evidence is provided that gene duplications were involved in the increase of genomic diversity of V alpha genes. In addition, we show a detailed map of a 40-kb region located approximately 100 kg upstream of the human C alpha gene. Direct evidence is provided to support that the human alpha chain locus, like the murine, also contains another T cell constant region gene in the alpha chain locus, the human delta chain gene. In addition, two J segments and one D segment have been identified. Using these genomic probes, we show that several T cell lines, including those known to express the surface gamma/delta heterodimer, have rearranged this region. The design of two separate centers of rearrangement within one locus that are involved in rearrangement events at different times, and the presence of high number of J segments in this region, may render the locus highly vulnerable to chromosomal translocation during T cell development.