A lymphocyte-specific enhancer in the mouse immunoglobulin κ gene

During differentiation of lymphocytes into antibody-producing cells, an immunoglobulin κ variable-region gene is transcriptionally activated by rearrangement linking it to a κ constant (Cκ) region gene which is already transcribed prior to somatic rearrangement1,2. The presence of a transcriptional enhancer element within the large intron of the κ light-chain gene has been postulated to explain this mode of activation, supported by evidence of a chromatin region which is preferentially accessible to DNase I3–5and restriction enzymes5. This DNA region contains a segment of about 130 base pairs (bp) which is strongly conserved between mouse, rabbit and man6. Moreover, no transcripts are detectable from a κ gene, which is truncated within the large intron7. Recently, a lymphocyte-specific enhancer has been identified downstream of the joining region in immunoglobulin heavy-chain genes8–10. We now show direct evidence for a functionally similar enhancer within the large κ gene intron of the mouse. It is, however, less active than the heavy-chain gene enhancer. In contrast, no enhancer was found to be associated with a cloned λI light-chain gene.