Roger Y. Tsien

Roger Y. Tsien was an American chemist who transformed green fluorescent protein, a naturally glowing protein first isolated from a species of jellyfish, into one of the most widely used tools in modern biological research. Building on earlier work by Osamu Shimomura, who first isolated the protein, and Martin Chalfie, who first showed it could be used as a genetic marker inside living cells, Tsien worked out in 1994 the chemical mechanism by which part of the protein's own structure folds up and reacts with itself to form the light-emitting chromophore responsible for its glow, without requiring any other special enzymes or added chemicals. Using this understanding, Tsien then engineered a wide palette of variant fluorescent proteins spanning the visible spectrum, including blue, cyan, yellow and red versions, by making targeted changes to the protein's structure, giving researchers a toolkit of different colored genetic markers that could be attached to separate proteins and tracked simultaneously within the same living cell. This work let biologists directly watch, in real time and in living tissue, where specific proteins are located and how they move and interact, transforming what had previously been possible only through static images of dead, chemically fixed cells. Tsien shared the 2008 Nobel Prize in Chemistry with Shimomura and Chalfie for the discovery and development of green fluorescent protein, and beyond GFP itself he also developed other widely used fluorescent chemical sensors, including indicators that let researchers directly visualize changing calcium levels inside living cells.