Move over GFP, it's FlAsH and ReAsH

Just read a paper that follows a viral protein in live cells using the smallest fluorescent tag available. In this paper they follow a protein that could not previously be labelled with a GFP tag. While extremely useful for many applications as a fluorescent tag to follow protein localization, GFP can disrupt the function of some proteins, thus defeating the purpose of labelling it in the first place. This recent paper makes use of a technology I had previously not heard of; biarsenical labelling of tetracysteine motifs. Tetracysteine motifs are exceedingly small, only six amino acids, and are therefore much less likely to disrupt protein function, however, they are still useful for affinity purification of your labelled protein. These amino acids then interact, non-covalently, with a biarsenical molecule which then greatly increases fluorescence of the molecule. Apparently this was originally found in 1998, and I just heard about it now. Invitrogen, a former sponser of the Bayblab (perhaps they don't approve of animal penises), sells the technology and, I presume, owns it aswell. The invitrogen website has a reasonable explanation of the commercially available system as well as links to the original references. Additionally there are some supplementary figures with movies using tetracysteine labelling technology, nothing extremely impressive or free access however.