In vivo occupancy of the kappa light chain enhancers in primary pro- and pre-B cells: A model for kappa locus activation

The immunoglobulin kappa light chain locus has two enhancer elements: the intronic enhancer, which lies between the J kappa cluster and the C kappa exon, and the 3'kappa enhancer, which is located downstream of C kappa. To address the contribution of these elements to the developmentally regulated activation of germline kappa locus transcription and rearrangement, we purified primary pro- and pre-B cells and determined by in vivo footprinting the sites within each enhancer that were occupied. We found that the kappa intronic enhancer NF-kappa B site is occupied in both pro- and pre-B cells, while CRE, BSAP, and PU.1/pip sites within the 3'kappa enhancer undergo changes in occupancy as cells progress from the pro-B to the pre-B cell stage. These findings suggest that regulation of the kappa locus in primary pre-B cells may be mediated by factors that bind the 3'kappa enhancer.