STIMULATION OF KAPPA-TRANSCRIPTION BY A DECAMER-DEPENDENT, SYNERGISTIC MECHANISM

The intact SP6 chi promoter stimulated transcription 30 times more eff iciently than did a control promoter consisting of a TATA motif as the only promoter element. Mutation of the SP6 chi promoter decamer in tw o positions reduced the transcriptional stimulation activity by over 9 0%. Promoters containing the SP6 chi promoter octamer or a consensus o ctamer in front of a TATA box were ineffective immunoglobulin promoter s and stimulated at the most 15% of maximal transcription. Identical r esults 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. Sele ctive mutations in the penta-decamer (pd), chi Y or early B cell facto r (EBF) elements of the promoter reduced transcriptional stimulation b y 20-30% in untransformed B cells. In S194 plasmacytoma cells the EBF mutation was functionally silent while the chi Y and pd mutations redu ced 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 ch i promoter function is highly dependent on complex interactions betwee n individual promoter elements and that the decamer motif is pivotal f or these interactions. The relative functional activity of a given pro moter varied according to the target cell population used for the func tional assay.