The discovery of GFP

Osamu Shimomura, a professor at the Princeton University, USA used to visit the US Pacific coast for summer vacations. There he collected many specimens of a jellyfish, Aequoria victoria. This fish was known to glow in the dark, with a bluish glow that turned green.

He succeeded in purifying the substance that caused this, and gave it the simple name of green fluorescent protein. A lot of scientists got interested in knowing why it was fluorescent. But they were looking for a way to produce the protein in bacteria, so that jellyfish did not have to be killed. Every protein is made from instructions written in a bit of DNA called a gene. Douglas Prasher of Woods Hole Oceanographic Institution was the first to succeed in putting the jellyfish gene in bacteria.

But he ran out of money to do any further research, and handed over the samples to Martin Chalfie of Columbia University. Now if you take a gene from one living thing and put it in another, most often it will not work correctly. But Chalfie was very lucky – not only did the gene work correctly, but the protein was made correctly and glowed green!

Many varieties of GFP have been made by genetic engineering, so that it now comes in many colours like red, yellow and blue. A company called Yorktown Technologies has created genetically modified fish that glow in many colours. These, called GloFish, are popular as aquarium pets in the USA.

Well, GFP glows green. So what?

Well, Douglas Prasher and Martin Chalfie had the idea that GFP could be attached to other proteins. Wherever the other protein would go, GFP would be dragged along. If you looked under a fluorescence microscope (which uses UV light instead of white light), you could see by the green glow where your protein was. GFP is in fact, acting like a spy!

GFP is widely used to study how a living thing develops. We all start life as one cell, that soon multiplies to make a body of millions of cells with different types of tissues. What tells a baby’s cell that it has to form liver tissue or brain tissue? The mixture of proteins in it tells that. But how do we know which protein is found in which cell?

Biotechnologists do that by tagging the GFP gene to genes for different proteins. These are then injected into the zygote. (That’s a word to describe an animal when it has just come into existence as a single cell). As the animal grows, different cells will go on to become different cells. If you saw that there was a green glow where the liver should be, then you know that the protein that was tagged with GFP is involved in making the liver!

And that’s how scientists have been figuring out how our genome, which has 30,000 genes, goes about making us!