In vivo transcriptional activation mediated through the −93/−84 binding site correlates with Sp1 expression. Five micrograms of either the −124 promoter-reporter construct (WT) or the −124 XN2mt construct (mut) were cotransfected into SL2 cells in triplicate along with the indicated amounts of either the pP_acSp1 expression plasmid or the empty pP_acU expression vector. The pCMV βgal plasmid was also cotransfected to normalize for transfection efficiency. Relative reporter activity was calculated as in Fig 4, with the activity of the pGL2:SV40 promoter plasmid assigned a value of 1; error bars indicate ± SE.