Courtesy of Promega

Have you ever needed a red fluorescent version of a protein, but only green was available? Promega http://www.promega.com of Madison, Wis., and Swiss company Covalys Biosciences http://www.covalys.com, have developed methods to tag proteins with a wide range of fluorescent dyes (and other ligands) by first fusing a protein of interest to a generic, nonfluorescent protein "handle." The handle binds covalently to an adapter on the ligand, linking the protein to the tag.

"You do only one cloning to get the fusion protein and then you expose the cell to different [ligands]," explains Covalys spokesperson Tom Gibbs, "whereas you have to reclone to get a different fusion protein for each variant of [green fluorescent protein]."

Currently available ligands enable labeling of fusion proteins in live or fixed mammalian cells or gels and isolating fusion proteins from complex mixtures. "But whenever we talk about this technology, our audience...

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