Use of caged fluorochromes to track macromolecular movement in living cells.

One way to visualize and track the movement of macromolecules in the living cell is to follow their movement after tagging the molecule with a 'caged' or chemically masked fluorochrome. The fluorochrome does not fluoresce until the caging group is released by spot photoactivation, and the bright fluorescent signal can then be tracked as it moves into the dark surrounding area of the cell. When coupled with rapid imaging microscopy, it is possible to measure rates of movement as fast as macromolecular diffusion. This article describes the use of photoactivatable fluorochromes to track the intracellular movement of both proteins and nucleic acids and to track cell lineages.