A TARGETED KAPPA-IMMUNOGLOBULIN GENE CONTAINING A DELETION OF THE NUCLEAR MATRIX ASSOCIATION REGION EXHIBITS SPONTANEOUS HYPER-RECOMBINATION IN PRE-B CELLS

Previous studies employing ectopic integration of reporter genes have shown that the nuclear matrix association region (MAR) adjacent to the intronic enhancer of the mouse re immunoglobulin (Ig) gene is require d for high level transcription of rearranged genes, demethylation, red uction of position effects and maximal somatic hypermutation in B cell s. To test for the function of this MAR in its natural chromosomal env ironment, we pursued the 'HIT-and-RUN' procedure with the mouse pre-B cell line 103 to create a targeted MAR deletion. We observed a 'HIT' t argeting frequency of 1/684 but 0/2100 'RUN' clones maintained the MAR -deleted germline locus because of an unexpected hyper-recombination f or V kappa-J kappa-joining, specifically to the MAR-deleted allele, an d primarily at J kappa 4 and J kappa 5. This hyper-recombination was c orrelated with undermethylation of the J kappa-C kappa region but not with the level of local transcription. These results are consistent wi th the possibility that the MAR and/or DNA methylation negatively regu late(s) V kappa-J kappa joining during the pre-B cell stage of develop ment. (C) 1998 Elsevier Science Ltd. All rights reserved.