Abstract
We have recently reported the localization of the first transcriptional enhancer in the human lambda (λ) immunoglobulin light chain locus. Enhancer activity was contained on a 1.2 kb
SstI fragment, with partial activity retained on a core 111 bp
PstI-
SstI fragment. This enhancer is located 11.7 kb downstream of Cλ7, the most 3′ lambda constant region gene. Using a chloramphenicol acetyl transferase (CAT) assay system, we have now determined the boundaries of the complete enhancer and find it is two- to four-fold as active as the core fragment in both pre-B and B cell lines. Interestingly, a larger fragment, containing the complete enhancer as well as 5′ and 3′ flanking sequences has four- to eight-fold reduced activity when tested in pre-B cell lines, but full activity in B cell lines. This suggests the presence of developmentally regulated negative elements flanking the human λ enhancer which prevent or reduce its activity at a developmentally incorrect time. By using
in vivo footprinting we have begun to examine the protein interactions within this enhancer in a more physiologically relevant manner and have identified motifs which are shared with the myrine λ enhancers, as well as motifs unique to the human λ enhancer.
