Glycosyltransferase assay. A to C, Quercetin (A) and its glucosides, quercetin-3-O-glucoside (B) and quercetin-7-O-glucoside (C), were separated by HPLC. D and E, Chromatograms of assay products using GST protein as a negative control (D) and AtGT-2 protein as a positive control (E). F, Chromatogram of OsGT1 reaction products. Peak Q, Quercetin; peak 3, quercetin-3-O-glucoside; peak 7, quercetin-7-O-glucoside. [See online article for color version of this figure.]