Functional modularity in the SP6 kappa promoter.

The requirements of the SP6 kappa promoter for transcriptional activation were studied in nontransformed murine B lymphocytes stimulated with lipopolysaccharide. Three different DNA motifs, besides the TATA-box, were needed for restoration of transcriptional activation to the same magnitude as seen with the native SP6 kappa promoter. The decamer motif (TNCTTTGCAT) was found to induce transcription alone and point-mutation of this element reduced transcription to negligible levels, although the other two required elements were present. The penta-decamer element (TGCAG/CCTGTGNCCAG) did not stimulate transcription alone, but activated transcription synergistically in conjunction with the decamer motif. This synergism required the presence of a third pyrimidine rich element (CCCT) in the decamer 3' flanking sequence. The pyrimidine rich element could partly be substituted for by an E-box core motif (CANNTG) 3' of, but not by the kappa Y motif (CTTCCTTA) 5' of, the decamer. Proteins interacting specifically with the penta-decamer element were detected by band-shift assay. The decamer 3' flanking sequence of the SP6 kappa promoter was found to modify the binding of endogenous Oct2 isoforms to the decamer motif i B lymphocytes, but not in CHO cells transfected with various Oct2 isoforms. Thus, complex protein/DNA interactions can be observed in the SP6 kappa promoter which correlate functionally with a synergism in transcriptional activation.