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Osamu Shimomura, Martin Chalfie, and Roger Tsien.

Source: The Nobel Foundation. Photo: U. Montan.

Many proteins are colored, but in most cases the color is generated by a prosthetic group (for example the heme group in hemoglobin (page 118) and in chlorophyll). However, in 1979 Osamu Shimomura, working at Princeton University in the USA, showed that the colored moiety in a GFP made by the jellyfish Aequorea aequorea was a reaction product of the amino acids themselves. This opened up the possibility of using the cell's own machinery to make genetically encoded labeling proteins that could be targeted to precise tissues and even specific sites within the cell. However, the suspicion was that one or more specialized enzymes in the jellyfish cells would be needed to carry out the conversion of the amino acids to the fluorophore, so that simply introducing the gfp gene would do nothing. In 1994 Martin Chalfie, working at Columbia University in New York, showed that this was not the case: the gfp gene product, on its own, converted itself into fluorescent GFP. The next leap in technology was to engineer GFP and GFP chimeras to be more than markers, and instead to be reporters of cell behavior. From 1992 onward, working at the University of California at San Diego, Roger Tsien and his lab engineered an ever‐increasing family of fluorescent proteins that are now used universally by cell biologists and drug companies to study almost all aspects of cell behavior, creating both beautiful science and beautiful images, such as Figure 1.15. Shimomura, Chalfie, and Tsien were awarded the Nobel Prize in Chemistry in 2008.

Answer to thought question: Only transmission electron microscopy reveals all the structures present in a particular volume of the cell at sufficient resolution to determine whether it is malformed. Super‐resolution microscopy has the resolution to reveal individual molecules on or within the Golgi, but only those individual molecules that the scientist chose to study are revealed, not the overall structure. Malformation of the endoplasmic reticulum and Golgi apparatus is thought to underlie one type of inherited spastic paraplegia.