The charged amino acids Arg218, Asp222, and Glu225 are indispensable for the AP1 epitope. Flow cytometry histograms of AP1 binding to mutations of the 3 charged residues, Arg218, Asp222, and Glu225, replaced with either Ala, with a residue of the same charge, or in the case of the 2 acidic residues, with the corresponding amides. Results are presented as histograms of the log fluorescence intensities of 10⁴ cells from the representative of 3 to 5 individual experiments.