Bimolecular fluorescence complementation (BiFC) analysis of protein interactions in live cells

Bimolecular fluorescence complementation (BiFC) analysis enables direct visualization of protein interactions and modifications in living cells. It is based on the facilitated association of two nonfluorescent fragments of a fluorescent protein fused to putative interaction partners. The intrinsic fluorescence of the active complex enables detection of protein interactions with high sensitivity, fine spatial resolution, and minimal perturbation of the cells. This protocol outlines methods to analyze protein interactions in cultured mammalian cells using BiFC, but can be readily adapted to any cell type or aerobically grown organism that can be genetically modified to express the fusion proteins.