Figure 2. Fluorogen activation approaches.

Binding of the fluorogen to an expressed domain can be used to release a quenching group (top), to bring a dye near to an environment that activates it, for example a membrane or protein pocket (middle), or to directly bind the fluorogen dye in a fluorescent complex (bottom). Direct binding of the fluorogen to the fluorogen activating protein is reversible, unlike cleavage or covalent linkage, which is advantageous for some applications.