Live-Cell Nucleocytoplasmic Protein Shuttle Assay Utilizing Laser Confocal Microscopy and FRAP

In eukaryotes, protein trafficking to and from the nucleus, or shuttling, has been demonstrated to be an important function for proteins that have vital roles in one or both subcellular compartments. Current techniques of detecting protein nuclear shuttling are extremely labor intensive and only statically visualize evidence of shuttling. Fluorescence recovery after photobleaching (FRAP), or fluorescence microphotolysis, has proven to be an effective method of analyzing protein dynamics in live cells, especially when coupled to GFP technology. Here, we describe a relatively simple in vivo protein nuclear shuttling assay that utilizes red fluorescent and green fluorescent protein fusions as substrates for FRAP using a laser confocal microscope. This technique is less time consuming than established shuttle assays, is internally controlled, and visualizes nucleocytoplasmic shuttling in living cells of the same species and cell type. This technique can be potentially used to detect the ability of any nuclear protein to shuttle from the nucleus to any other subcellular compartment for any eukaryotic species in which GFP or dsRed1 fusion protein can be expressed.