Unusual organization and diversity of T-cell receptor a-chain genes

Abstract

T lymphocytes recognize cell-bound antigens in the molecular context of the self major histocompatibility complex (MHC) gene products through the surface T-cell receptor(s). The minimal component of the T-cell receptor is a heterodimer composed of α and β subunits, each of relative molecular mass (M_r)∼ 45,000 (refs 1–3). Recently, complementary DNA clones encoding these sub-units have been isolated and characterized along with that of a third subunit of unknown function, termed γ (refs 4–9). These studies revealed a primary structure for each subunit that was clearly similar to that of immunoglobulin and indicated a somatic rearrangement of corresponding genes that are also immunoglobulin-like. Recently, the analysis of the sequence organization of the T-cell receptor β-chain^10–16 and T-cell-specific γ-chain gene families¹⁷ has been reported. We now present an initial characterization of the murine T-cell receptor α-chain gene family, and conclude that although it is clearly related to the gene families encoding immunoglobulins¹⁸, T-cell receptor β-chains^10–16 and also T-cell γ-chains¹⁷, it shows unique characteristics. There is only a single constant (C) region gene segment, which is an exceptionally large distance (∼20–40 kilobases (kb) in the cases studied here) from joining (J) gene segments. In addition, the J cluster and the variable (V) segment number seem to be very large. Finally, in the case studied here, a complete α-chain gene shows no somatic mutation and can be assembled directly from V_α, J_α and C_α segments without inclusion of diversity (D_α) segments.