The kindling fluorescent protein: a transient photoswitchable marker.

Passive fluorescent protein markers are indispensable for dynamic cellular imaging; however, they are unselective, introduce constant background fluorescence, and require continuous observation. Photoactivatable fluorescent proteins have now been developed whose fluorescence can be switched on and off by illumination, allowing selective and direct tracking of tagged objects without the need for continuous imaging. The "kindling fluorescent protein" is a photoactivatable marker with a novel twist: it turns itself off after a selectable period.