The germline promoter region upstream of the Dβ1 gene segment in the murine TCRβ locus was deleted to assess its role in controlling V(D)J recombination. Associated with diminished Dβ1 region germline transcription, rearrangement of the Dβ1 but not the Dβ2 gene segment was reduced 10- to 20-fold. A corresponding reduction in RAG-mediated cleavage at the Dβ1 and Jβ1 signal sequences was apparent only when purified CD4-CD8- thymocytes were analyzed because, as we demonstrate, cleavage at these gene segments also occurred in CD4+CD8+ thymocytes. These findings suggest that germline promoters regulate localized accessibility of gene segments for recombination and that in CD4+CD8+ thymocytes TCRβ allelic exclusion does not result from inaccessibility of Dβ gene segments.
Whitehurst, C. E., Chattopadhyay, S., & Chen, J. (1999). Control of V(D)J recombinational accessibility of the Dβ1 gene segment at the TCRβ locus by a germline promoter. Immunity, 10(3), 313–322. https://doi.org/10.1016/S1074-7613(00)80031-X