Connexin the dots

New dyes developed by Guido Gaietta, Roger Tsien, Mark Ellisman (University of California at San Diego, La Jolla, CA), and colleagues allow efficient fluorescent and electron microscopy for studying the location, trafficking, assembly, and turnover of proteins and protein complexes.“We were interested in being able to go from light microscopy to the EM level,” says Ellisman. “In particular, we wanted better resolution than with immunogold labeling.” To do so, the group examined FlAsH, a biarsenical derivative of fluorescein. FlAsH binds to small amino acid extensions containing the sequence C-C-X-X-C-C, which can be added to recombinant target proteins. Binding of FlAsH causes the ligand to emit a strong green fluorescence, and binding of ReAsH, a red variant, leads to red fluorescence.

ReAsH is the variant that is useful for EM, because it can...