Qualitative changes in the subunit composition of kappa B-binding complexes during murine B-cell differentiation.

We report here that the major kappa B-binding complex in murine mature B cells is composed of a p50-Rel heterodimer, whereas the major inducible form in pre-B cells is a p50-p65 heterodimer. Treatment of a pre-B-cell line with lipopolysaccharide changes the subunit composition of kappa B-binding complexes from p50-p65 to p50-Rel. This change is preceded by the enhanced Rel expression and correlates with the expression of the gene for the immunoglobin kappa light chain. The heterodimeric p50-Rel complex binds to the intronic enhancer-kappa B site in the immunoglobulin kappa light chain gene at least 20-fold more stably than does the p50-p65 dimer. These data support a model in which augmentation of Rel expression during the differentiation of pre-B cells to mature B cells leads to an exchange of kappa B-binding subunits resulting in the transcriptional activation of the gene for the immunoglobulin kappa light chain.