Green becomes red

Today's reef-building corals cover shallow blue seas around the world in a giant living Technicolor blanket. And the corals' fluorescent greens, blues, reds, yellows and oranges back a vast stage on which a reef's other multicolored, finned inhabitants play.

Coral fluorescence is caused by special fluorescent proteins, and researchers have just figured out how -- mutation by mutation -- one of the red fluorescent proteins evolved from the green protein of ancestral corals. They did so by looking back in time -- "resurrecting" a large number of possible fluorescent proteins that may have been the intermediate steps in the green-to-red evolution.

"This resurrection method is actually quite a sci-fi thing, something like 'Jurassic Park,'" saidĀ Mikhail Matz, assistant professor of integrative biology.

But actually, the resurrection process is even more interesting than that fictionalized in the book.

Matz didn't slurp out old DNA or proteins from the skeletons of ancient corals and rebuild new organisms. Instead, he and research assistant Steven Field came up with the potential recipes for making the ancestral proteins by running computations on the present day red fluorescent protein. Then, they synthesized and expressed the genes for these candidate "missing link" proteins in bacteria in the lab. The various fluorescent proteins are active in the bacteria, so the microbes glow under the right light conditions just like coral.

Matz and Field found that it took about 12 mutations -- or changes in the protein sequence -- for the ancestral green to evolve into the red (see spiral image).

Five of the 12 mutations the scientists found would have been missed by traditional methods of analysis, proving that reconstructing ancestral proteins in this way can lead to novel insights about molecular evolution.

"Our results illustrate the need for back-in-time analysis of protein function," Matz said. "If we would have been comparing currently existing greens to reds, we would have missed half of the historically essential mutations."

The research was published online Sept. 30, in the journalĀ Molecular Biology and Evolution.