B-CELL-SPECIFIC DEMETHYLATION - A NOVEL ROLE FOR THE INTRONIC KAPPA-CHAIN ENHANCER SEQUENCE

We studied the molecular mechanism of demethylation and its role in ka ppa chain gene regulation. Following transfection into B cell cultures , this gene undergoes regional demethylation in a process that is deve lopmentally regulated in a lineage- and stage-specific manner. Althoug h a germline V kappa promoter is not required for the demodification a ctivity, a fragment containing the intronic kappa chain transcriptiona l enhancer and the nearby matrix attachment region is essential. In it s natural location downstream to the J kappa 5 sequence, this element induces bidirectional demodification of plasmid constructs in a distan ce- and orientation-independent manner. When this enhancer is placed i n an upstream position, however, the kappa gene remains modified and t ranscriptionally inactive, demonstrating that demethylation is require d for kappa chain activation. These studies suggest that the kappa enh ancer plays a dual role in regulating B cell differentiation by induci ng demethylation and by promoting tissue-specific transcription.