What is "snap-tag"

thumb|500px|SNAP-tag reaction scheme SNAP-tag is a self-labeling protein tag commercially available in various expression vectors. SNAP-tag is a 182 residues polypeptide (19.4 kDa) that can be fused to any protein of interest and further specifically and covalently tagged with a suitable ligand, such as a fluorescent dye. Since its introduction, SNAP-tag has found numerous applications in biochemistry and for the investigation of the function and localisation of proteins and enzymes in living cells. Compared to the current standard labelling methods used in fluorescence microscopy, the use of SNAP-tag presents significant advantages.