Analysis of protein dynamics in living cells by FRAP. (a) FRAP experiment. A small area in the nucleus of a cell expressing a fluorescent protein (1) is irreversibly photobleached with a laser beam (2), and the recovery of the fluorescence intensity due to entry of non-photobleached molecules (orange arrows) is continuously monitored (3 and 4).
(b) Hypothetical plots for fast and slow fluorescence recovery (high and low mobility, respectively). The rate of recovery is inversely related to the time that a protein is bound to chromatin13,66.