Labeling reaction using SNAP-Vista Blue

Protocol

1. Add 2 µl of the substrate stock solution to 18 µl of protein sample containing a SNAP-Tag fusion protein in an appropriate buffer (see notes). Mix well by pipetting up and down several times.
2. Incubate in the dark for 20 min at 25°C.
3. Add an appropriate volume of concentrated SDS-PAGE sample buffer and proceed with sample preparation and running the SDS-PAGE gel according to the gel manufacturer’s instructions.
4. It may be useful to run prestained fluorescent molecular weight markers on the gel.
5. After the gel is run, you should immediately take a fluorescent image using a UV-transilluminator and an appropriate camera (Polaroid or digital). The dye is well suited for 360 nm excitation. The fluorescence is an intense blue.
   
   After fluorescent imaging, you can use your usual fixing and staining protocols to detect the non-fluorescent proteins.