EARLY B-CELL FACTOR INTERACTS WITH A SUBSET OF KAPPA-PROMOTERS

A conserved sequence element situated between the decamer and TATA box in V kappa II and V kappa V promoters has a high homology to the bind ing site for early B cell factor (EBF). The kappa promoter element was shown to bind EBF specifically using both in vitro-translated protein and nuclear extract. Concomitant binding of EBF and Oct proteins to a wild-type kappa promoter template was observed at low efficiency, and such dual occupancy was dependent on an intact amino terminus of the Oct protein. When the two binding sites were separated by a 10-bp spac er, this dependency disappeared. A single kappa promoter EBF site toge ther with a TATA box and an Ig heavy chain enhancer showed marginal tr anscriptional stimulatory activity. In contrast, the EBF site acted sy nergistically with a decamer element in EBF-negative plasmacytoma cell s, but not in B cells of an earlier differentiation stage. In these ce lls, a distinct protein was observed that interacted with the EBF bind ing motif, while overexpression of EBF downregulated the expression of a reporter construct containing Ig control elements.