Site-directed mutagenesis of the tandem AP1 binding sites markedly reduced the promoter/enhancer activity of the intact p₂2592-CAT construct. Mutation of the 5′ AP1 site, the 3′ AP1 site, or both AP1 sites was introduced into the original p₂2592-CAT construct by site-directed mutagenesis. The promoter/enhancer activity of the original p₂2592-CAT construct was compared with the activity of the construct with mutations in the 5′AP1 site, the 3′ AP1 site, or both AP1 sites after transient transfection into uninduced and induced K562 cells and uninduced and induced DAMI cells. Cotransfection with RSV-luciferase was used to control for transfection efficiency. After 48 hours of incubation, cell extracts were assayed. After normalization for transfection efficiency, CAT activity of the constructs was determined by thin-layer chromatography and differential extraction. The mean and standard deviation of CAT activity of the mutant constructs in either K562 cells or DAMI cells from at least three separate electroporations was determined relative to the pCAT-Basic construct in uninduced K562 or uninduced DAMI cells, respectively, which was assigned a value of 1.0.