Activating photoactivatable proteins with laser light to visualize membrane systems and membrane traffic in living cells.

Eukaryotic cells are composed of an intricate system of internal membranes that are organized into different compartments--including the endoplasmic reticulum (ER), the nuclear envelope, the Golgi complex (GC), lysosomes, endosomes, caveolae, mitochondria, and peroxisomes--that perform specialized tasks within the cell. The localization and dynamics of intracellular compartments are now being studied in living cells because of the availability of green fluorescent protein (GFP)-fusion proteins and recent advances in fluorescent microscope imaging systems, such as the confocal laser-scanning microscope (CLSM). This protocol describes the steps for activating one of the first photoactivatable proteins, PA-GFP.