AbstractThe intact SP6 χ 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 χ promoter decamer in two positions reduced the transcriptional stimulation activity by over 90. Promoters containing the SP6 χ 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), χY 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 χY 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 χ 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 f
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