Stimulation of kappa transcription by a decamer-dependent, synergistic mechanism

The intact SP6 kappa promoter stimulated transcription 30 times more efficiently than did a control promoter consisting of a TATA motif as the only promoter element. Mutation of the SP6 kappa promoter decamer in two positions reduced the transcriptional stimulation activity by over 90%. Promoters containing the SP6 kappa promoter octamer or a consensus octamer in front of a TATA box were ineffective immunoglobulin promoters and stimulated at the most 15% of maximal transcription. Identical results were obtained after transfection of untransformed mouse splenic B cells stimulated by lipopolysaccharide, that express high levels of Oct2A, or of S194 cells that express negligible levels of Oct2A. Selective mutations in the penta-decamer (pd), kappa Y or early B cell factor (EBF) elements of the promoter reduced transcriptional stimulation by 20-30% in untransformed B cells. In S194 plasmacytoma cells the EBF mutation was functionally silent while the kappa Y and pd mutations reduced transcriptional activation by 60-70% in this cell line. A mutation in a TATA-proximal E-box motif did not alter the functional activity of the promoter in either cell population. It can be concluded that kappa promoter function is highly dependent on complex interactions between individual promoter elements and that the decamer motif is pivotal for these interactions. The relative functional activity of a given promoter varied according to the target cell population used for the functional assay.