Genomic organization of the human T-cell antigen-receptor α/δ locus

Two clusters of overlapping cosmid clones comprising about 100 kilobases (kb) at the human T-cell antigen-receptor α/δ locus were isolated from a genomic library. The structure of the germ-line V(δ)1 variable gene segment was determined. V(δ)1 is located 8.5 kb downstream of the V(α)13.1 gene segment, and both V segments are arranged in the same transcriptional orientation. The V(α)17.1 segment is located between V(δ)1 and the D(δ), J(δ), C(δ) region (containing the diversity, joining, and constant gene segments). Thus, V(δ) and V(α) segments are interspersed along the chromosome. The germ-line organization of the D(δ)2, J(δ)1, and J(δ)2 segments was determined. Linkage of C(δ) to the J(α) region was established by identification of J(α) segments within 20 kb downstream of C(δ). The organization of the locus was also analyzed by field-inversion gel electrophoresis. The unrearranged V(δ)1 and D(δ), J(δ), C(δ) regions are quite distant from each other, apparently separated by a minimum of 175-180 kb.