Regulation of V(D)J recombination by transcriptional promoters

Enhancer elements potentiate the rearrangement of antigen receptor loci via changes in the accessibility of gene segment clusters to V(D)J recombinase . Here, we show that enhancer activity per se is insufficient to target T-c ell receptor beta miniloci for D beta J beta recombination, Instead, a prom oter situated 5' to D beta 1 (PD beta) was required for efficient rearrange ment of chromosomal substrates, A critical function for promoters in regula ting gene segment accessibility was further supported by the ability of het erologous promoters to direct rearrangement of enhancer-containing substrat es, Importantly, activation of a synthetic tetracycline-inducible promoter (Ptet) positioned upstream from the D beta gene segment was sufficient to t arget recombination of miniloci lacking a distal enhancer element. The latt er result suggests that DNA loops, generated by interactions between flanki ng promoter and enhancer elements, are not required for efficient recogniti on of chromosomal gene segments by V(D)J recombinase, Unexpectedly, the Pte t substrate exhibited normal levels of rearrangement despite its retention of a hypermethylated DNA status within the D beta J beta cluster, Together, our findings support a model in which promoter activation, rather than int rinsic properties of enhancers, is the primary determinant for regulating r ecombinational accessibility within antigen receptor loci.