The immunoglobulin kappa locus contains a second, stronger B-cell-specific enhancer which is located downstream of the constant region.

The description of cell lines capable of transcribing immunoglobulin heavy or light chain genes in the apparent absence of an active enhancer has led us to look for novel enhancers in the immunoglobulin gene loci. Here we show that there is a second B-cell-specific enhancer in the mouse kappa locus and that this is located 9 kb downstream of C kappa. This enhancer is some 7-fold stronger than the kappa-intron enhancer and shows striking sequence homologies to the lymphotropic papovavirus, IgH and kappa-intron enhancers. The location of the kappa 3' enhancer between C kappa and the RS element means that it is deleted in some B cells that express lambda light chains.