Identification of genes for the constant region of rabbit T-cell receptor beta chains

We describe cDNA clones from thymus mRNA of a young rabbit that have sequences highly homologous to the human and murine T-cell receptor beta-chain constant region (C beta). In rabbit, man, and mouse there is a conserved extra cysteine in the constant region that could lead to a free thiol group or alternative disulfide bond formation depending on the locations and total numbers of cysteines in assembled receptor molecules. A cDNA clone (CL ANA 11) with 571 bases 5' of the C beta coding sequence has an open reading frame starting at a methionine codon that encodes 141 amino acids in frame with the C beta sequence. The encoded sequence has no resemblance to known immunoglobulin or beta-chain variable regions or other known proteins. An oligonucleotide probe from the 5' end of the encoded protein hybridizes to an approximately equal to 2-kilobase genomic DNA fragment that contains C beta gene sequences and to an approximately equal to 8-kilobase mRNA species in the thymus mRNA preparation from which the clone was derived. Within the 5' coding sequence there is a stretch of 211 bases containing strings of alternating purines and pyrimidines that may form Z-DNA. The sequence of the last 55 base pairs adjacent to C beta resembles the corresponding segment of mouse cDNA clone 86T3 that contains sequence 5' of the mouse C beta 1 gene. Although the function of a potential protein encoded by the 5' end of CL ANA 11 is unknown, it could play a role in regulation of thymocyte growth and differentiation.