The general structure of rearranged TCR genes is shown in Figure 9-7. The variable regions of T-cell receptors are, of course, encoded by rearranged VDJ and VJ sequences. In TCR genes, combinatorial joining of V gene segments appears to generate CDR1 and CDR2, whereas junctional flexibility and N-region nucleotide addition generate CDR3. Rearranged TCR genes also contain a short leader (L) exon upstream of the joined VJ or VDJ sequences. The amino acids encoded by the leader exon are cleaved as the nascent polypeptide enters the endoplasmic reticulum.
The constant region of each TCR chain is encoded by a C gene segment that has multiple exons (see Figure 9-7) corresponding to the structural domains in the protein (see Figure 9-3). The first exon in the C gene segment encodes most of the C domain of the corresponding chain. Next is a short exon that encodes the connecting sequence, followed by ex-ons that encode the transmembrane region and the cytoplas-mic tail.
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