V(D)J recombination and allelic exclusion of a TCR β-chain minilocus occurs in the absence of a functional promoter

Transcriptional activation of rearranging Ag receptor gene segments has been hypothesized to regulate their accessibility to V(D)J recombination. We analyzed the role of a functional promoter in the rearrangement of the murine TCR β-chain locus using two transgenic minilocus constructs. These miniloci each contain an unrearranged Vβ8.3 gene. One has a wild-type Vβ8.3 gene, but the other has a Vβ8.3 gene with a promoter mutation that was previously shown to abrogate transcription in tissue culture. FACS analysis of thymus and lymph node cells from transgenic mouse lines showed that only the lines with the wild-type Vβ8.3 gene promoter express an 8.3 TCR β-chain. Consistent with the protein expression data, Vβ8.3 gene transcripts were found only in the transgenic lines with the wild-type promoter. Using a quantitative PCR-based assay, it was shown that both types of transgenic lines recombine the Vβ8.3 gene at similar levels. Rearrangement of the transgenes was normal with respect to thymic development and junctional reading frame. Interestingly, both types of miniloci also underwent allelic exclusion in that recombination was blocked by the expression of a rearranged TCR β-chain transgene. We conclude that a functional Vβ gene promoter is not necessary for proper V(D)J recombination to occur.