Nucleocytoplasmic shuttling revealed by FRAP and FLIP technologies.

Protein mobility within cells is of key importance for many cellular functions. Although immunostaining can reveal protein locations in the steady-state, this might not represent the full picture and provides no information about protein movements. Fluorescence recovery after photobleaching (FRAP) and fluorescence loss in photobleaching (FLIP) are two techniques that enable the dynamics of intracellular protein mobility to be studied. These technologies have been successfully used to analyze the nucleocytoplasmic shuttling of STAT1, an intracellular signal transducer and activator of transcription, and can applied to the study of other proteins. Furthermore, FRAP and FLIP approaches have the added advantage of not affecting cell viability and might find application in the imaging of intracellular events in certain tissues and live animals.