Mutational analysis of the CCAAT box region of the γ-globin promoter. The indicated base substitution mutations were introduced into the −198 γ-globin-CAT plasmid in the distal (A) or the proximal (B) CCAAT box. Transfections were performed as usual, and cells were left untreated (□) or treated with 1 mmol/L arginine-butyrate (▪), 2.5 nmol/L trapoxin (▧), or 100 nmol/L trichostatin () as indicated. CAT activity is expressed relative to the activity of the −198 construct (WT). The data shown are the average of two or three transfections done with each construct; error bars show the standard deviation where three trials were done.