Alteration of a single nucleotide allows efficient binding of H2TF1/KBF1 to the immunoglobulin kappa enhancer B motif.

NF-kappa B (a protein present constitutively only in B cells) and H2TF1/KBF1 (a more ubiquitously distributed protein[s]) are two transcription factors that recognize very similar DNA sequences. However, the binding site associated with the kappa immunoglobulin gene enhancer (kappa B) is recognized predominantly by NF-kappa B. Using synthetically altered recognition sequences, we showed that the B-cell-specific NF-kappa B-binding site in the kappa enhancer can be converted to one that binds both NF-kappa B and the ubiquitous protein(s) H2TF1/KBF1 by substitution of a single nucleotide. Furthermore, transient transfection experiments suggested that NF-kappa B and H2TF1/KBF1 are functionally different even though their DNA recognition specificities are very similar.