The 3' enhancer region determines the B/T specificity and pro-B pre-B specificity of immunoglobulin V-kappa-J(kappa) joining

Using transgenic substrates, we found that the immunoglobulin kappa gene 3' enhancer (E3') acts as a negative regulator in V-kappa-J(kappa) joining. Although the E3' was originally identified as a transcriptional enhancer, it acts in a suppressive manner for recombinational regulation. Base substitution analysis has shown that the PU.1-binding site within the E3' regulates the B/T specificity of V-kappa-J(kappa) joining. In a substrate with a mutated PU.1-binding site (GAGGAA to TCTTCG), V-kappa-J(kappa) joining occurred not only in B cells, but also in T cells. The E3' region is also responsible for determining the pro-B/pre-B specificity of V-kappa-J(kappa) joining. When the E3' region was deleted, kappa gene rearrangement actively occurred at the early pro-B stage of B cell development: nongermline (N) nucleotides were common at recombination junctions.