For a team at the University of California, San Diego, nine years of tinkering with arsenic paid off in the development of a new technique that can tag proteins with different colors over time and even zero in to electron microscopic resolution. Roger Tsien, Howard Hughes Medical Institute investigator and professor of pharmacology, chemistry, and biochemistry at UCSD, says the project started with the suggestion from a colleague that one can tag a two-cysteine sequence in a protein with a single arsenic. "A little reading convinced me it wasn't specific enough as it was. We had to come up with a way that made it much tighter," says Tsien.
They came up with a process in which researchers engineer a tetracysteine sequence (Cys Cys Xaa Xaa Cys Cys) into a protein and expose cells to a small, biarsenical derivative of fluorescein called FLAsH, which is green under a fluorescent...
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