IN-VIVO OCCUPANCY OF THE KAPPA-LIGHT-CHAIN ENHANCERS IN PRIMARY PRO-BAND 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 develop mentally regulated activation of germline kappa locus transcription an d rearrangement, we purified primary pro- and pre-B cells and determin ed by in vivo footprinting the sites within each enhancer that were oc cupied. We found that the kappa intronic enhancer NF-kappa B site is o ccupied in both pro- and pre-B cells, while CRE, BSAP, and PU.1/pip si tes within the 3'kappa enhancer undergo changes in occupancy as cells progress from the pro-B to the pre-B cell stage. These findings sugges t that regulation of the kappa locus in primary pre-B cells may be med iated by factors that bind the 3'kappa enhancer.