Regulation of V(D)J recombination: A dominant role for promoter positioning in gene segment accessibility

Antigen receptor gene assembly is regulated by transcriptional promoters and enhancers, which control the accessibility of gene segments to a lymphocyte-specific V(D)J recombinase. However, it remained unclear whether accessibility depends on the process of transcription itself or chromatin modifications that accompany transcription. By using T cell receptor beta substrates that integrate stably into nuclear chromatin, we show that promoter location, rather than germ-line transcription or histone acetylation, is a primary determinant of recombination efficiency. These spatial constraints on promoter positioning may reflect an RNA polymerase-independent mechanism to target adjacent gene segments for chromatin remodeling events that facilitate rearrangement.