Expression of a TCR V_β8.2 polypeptide from the unrearranged gene in a murine lymphoid precursor cell line

The TCR in a mature T cell is a multimeric complex of TCR α and β chains, and CD3 subunits. Functional TCR α and β chains are encoded by genes that result from developmentally controlled somatic rearrangement events. By FACS analysis, we have detected a TCR V_β8 protein on the surface of an immature lymphoid cell line, C1-V13D, that has all of its TCR genes in germline(unrearranged) configuration. RNA blot analysis detected a 1.4 kb polydenylated V_β8 RNA in C1-V13D cells, but no expression of C_β was detected. Rapid amplification of 3' cDNA ends was used to clone an RNA that was initiated from the leader exon of the V_β5.1 gene and spliced to the V exon of the V_β8.2 gene. The putative sequence of the mature 10.8 kDa protein was entirely encoded by the V_β8.2 exon. RT-PCR analysis confirmed that 97% of the V_β8 RNA detected in C1-V13D cells was encoded by the V_β8.2 gene, and only 3% by V_β8.1 and V_β8.3 genes. Furthermore, most of the V_β8.2 RNA was spliced to the leader exon of the V_β5.1 gene and not to the leader exon of the V_β8.2gene. The implications of preferential transcription from particular germline TCR genes for repertoire diversity and possible functions for proteins translated from germline TCR V_β genes are discussed.