Identification and localization of an enhancer for the human λ L chain Ig gene complex

A strong transcriptional enhancer was identified for the human λ L chain Ig gene complex. Enhancer activity was measured by activation of the chloramphenicol acetyl transferase (CAT) gene in a transient assay using both mouse and human B lymphoid cell lines. The smallest fragment identified with enhancer activity was 111 bp, which resides 11.7 kb downstream (3′) of Cλ7, a constant region gene we have recently isolated and identified as functional in the human population. Enhancer activity is orientation independent, tissue specific (active in all B cell lines tested and not in a T cell line), and independent of NFκB, similar to the mouse λ enhancers recently reported. The human λ enhancer is active in both mouse and human B cell lines; interestingly, the mouse λ enhancers are active in mouse lines but not in a human B cell line. DNA sequence comparison of the mouse and human λ enhancers indicates a higher degree of homology (average of 72.5%) within the 111-bp enhancer core region identified here than for the remaining flanking sequence compared (average of 42%). This discovery of an enhancer in the human λ locus (HuEλ), which is clearly distinct from that of the H and L chain loci, will help to determine the mechanism for the ordered expression and rearrangement of these gene complexes in B cell ontogeny. The presence of only one enhancer in the human Cλ complex 3′ of all the C genes suggests that the evolutionary duplication of the L locus differs from that seen in mouse; in mouse the duplication unit was JCJC-enhancer, whereas the human JCλs duplicated without the enhancer.