Sequence and evolution of the human T-cell antigen receptor beta-chain genes.

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Abstract
The nucleotide sequences of the 2 genomic constant (C)-region gene segments, C.beta.1 and C.beta.2, encoding the .beta. chain of the human T cell antigen receptor are presented. The 2 C.beta. genes are organized identically to each other and to the corresponding mouse genes, both having 4 exons, whose boundaries were confirmed from the sequence of a C.beta.2 complementary DNA clone from the T cell line MOLT-4. The predicted amino acid sequences of human C.beta.1 and C.beta.2 differ at only 5 positions, which suggests that the proteins have very similar functions. This similarity is the result of strong nucleotide-sequence conservation in protein-coding regions, which extends to silent positions. A quantitative analysis of an alignment of the nucleotide sequences of the 2 human genes shows that whereas the 5'' ends (including the 1st exon) are extremely homologous, the 3'' ends are widely divergent, with other regions having intermediate levels of homology. Analysis of published data shows that the mouse C.beta.1 and C.beta.2 genes are also virtually identical in their 1st exons but more divergent in the remaining coding regions. Therefore, partial gene conversion events may have occurred during the evolution of both human and mouse C.beta. genes.