Figure 1.

Labeling strategies and representative fluorescent labels 1–17. The fluorophoric portions of ligands are colored according to emission maxima of the dye. (A) Molecules with intrinsic binding affinity for native cellular biomolecules and subcellular regions. (B) Genetically encoded fluorescent proteins. (C) Affinity-based tag–ligand systems with a genetically encoded binding element. (D) Enzyme-based “self-labeling” tag–ligand system. (E) Enzyme-based tag–ligand system based on posttranslational modification.