GFP and SNAP-tags are both valuable technologies used to visualize proteins in live cells. GFP is an intrinsically fluorescent protein derived from Aequorea victoria while SNAP-tag is derived from hAGT, a human DNA repair protein. In contrast to GFP, the fluorescence of SNAP-tag fusions can be readily turned on with the addition of a variety of fluorescent probes added directly to the culture media. Substituting different fluorophores or other functionality (biotin, magnetic beads, blocking agents) requires no new cloning or expression, merely incubation of the appropriate substrate with cells, cell lysates or recombinant proteins. Click here to see a comparison of SNAP-tag and GFP.