Post-transcriptional allelic exclusion of two functionally rearranged T cell receptor α genes

We cloned and sequenced T cell receptor (TCR) α and β chain cDNA from a λgt10 library obtained from a murine I-A^k autoreactive helper T cell clone MS202. Two types of cDNA clones for the α chain and one for the β chain were obtained. The two α chain transcripts used two different V_α genes: V_{α 4,} joined to J_{α 11.2;} and V_{α 5,} joined to J_αTA13. The four V_α4 cDNA clones obtained did not have a complete sequence, lacking the leader portion. The V_α4 genomic gene segment of MS202 was revealed to contain two exons corresponding to the V_α4.MD13 cDNA sequence, and the potential RNA splicing signals between the two exons were Intact. Both of the a chain cDNA clones showed In-frame rearrangements. Immunoprecipitation of ¹²⁵I-surfacelabeled lysate of MS202 with anti-TCR antiserum and subsequent electrophonetic analyses indicated that only one of the α chain polypeptides was expressed on the cell surface. Thus, allelic exclusion of the α chain in MS202 is achieved by post-transcriptional regulation rather than rearrangements.