Regulation of T cell receptor β gene rearrangements and allelic exclusion by the helix-loop-helix protein, E47

Allelic exclusion of antigen-receptor genes is ensured primarily by monoallelic locus activation upon rearrangement and subsequently by feedback inhibition of continued rearrangement. Here, we demonstrated that the basic helix-loop-helix protein, E47, promoted T cell receptor beta (TCR beta) gene rearrangement by directly binding to target gene segments to increase chromatin accessibility in a dosage-sensitive manner. Feedback signaling abrogated E47 binding, leading to a decline in accessibility. Conversely, enforced expression of E47 induced TCR beta gene rearrangement by antagonizing feedback inhibition. Thus, the abundance of E47 is rate limiting in locus activation, and feedback signaling downregulates E47 activity to ensure allelic exclusion.