Fluorescent proteins are invaluable tools for measuring the abundance and trafficking of other proteins in a cell. A bigger challenge has been to monitor a protein’s life cycle—its intracellular movements and its turnover—which requires a timer to indicate a protein’s age. Earlier iterations of fluorescent timers used one protein that changed color over time, “but this is at the expense of sensitivity and brightness,” says Michael Knop of the University of Heidelberg.
To improve upon the idea of a fluorescent timer, Knop and his colleagues fused two different fluorescent proteins to produce a timer that glows with different colors and intensities depending on the age of the target protein. The first of the fluorescent proteins, superfolder GFP (sfGFP), reaches peak intensity very quickly, while the ...
