Identification of Genes for the Constant Region of Rabbit T-Cell Receptor β 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 β -chain constant region (Cβ). 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 Cβcoding sequence has an open reading frame starting at a methionine codon that encodes 141 amino acids in frame with the Cβsequence. The encoded sequence has no resemblance to known immunoglobulin or β -chain variable regions or other known proteins. An oligonucleotide probe from the 5′end of the encoded protein hybridizes to an ≈ 2-kilobase genomic DNA fragment that contains Cβgene sequences and to an ≈ 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 Cβresembles the corresponding segment of mouse cDNA clone 86T3 that contains sequence 5′of the mouse Cβ 1gene. 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.