FIGURE 2 Thin-layer chromatography to detect chemically modified nucleotides. (a) RNase-digested tRNA is spotted onto a silica-coated glass plate, and solvent and nucleotides migrate up the plate by capillary action. (b) Modified and unmodified nucleotides—in this case, pseudouridine monophosphate (ψMP) and UMP, as control—migrate at different rates, based on their different solubilities in the solvent and their different affinities for the silica gel.