Triumph of the Helix
In an epochal discovery 50 years ago, life met its own master molecule
Today's DNA, for example, uses 20 different three-letter "words" to code for the building blocks of proteins, called amino acids. But why stop at 20? Last month, Mehl and Peter Schultz's group at Scripps reported that they had managed to write a new word in ordinary DNA, coding for an unnatural, 21st amino acid. They slipped the altered word into a gene for a protein called myoglobin, then inserted the modified gene into the DNA of bacteria. They also engineered the bacteria to make their own supply of this unnatural amino acid. The result: bacteria that could independently produce an unnatural form of myoglobin. The group is now pitting bacteria with this extra DNA word against bacteria without it to see which can adapt better to new conditions.
Other groups hope to expand DNA's four-letter alphabet. Floyd Romesberg's group at Scripps has created extra chemical letters and slipped them into DNA in a test tube. Now they're trying to get the altered DNA into living bacteria. Romesberg wants to see what a cell would do with an extra chemical letter in times of stress or need. His ultimate plan, he says, is to "give the bugs freedom and let them run with the ball. Give them an evolvable system and sort of let them go."
Some scientists have a far more radical fantasy: creating a completely novel chemical that could do everything needed for life. "I dream of coming up with an unnatural genetic molecule and an unnatural protein that copies it," says Stanford's Kool. "I don't think there's any question that would be life."
But he has no illusions that it will be easy to come up with a rival for the double helix. For the foreseeable future, it seems, DNA will still reign supreme--at least on the planet we call home.
Home-Brewed DNA
DNA is all around you, and you don't need a Ph.D. to extract it. You will need a source of DNA (any living matter will do, but strawberries work well), salt (the noniodized kind), shampoo, and 90 percent rubbing alcohol (chilled in the freezer).
1. Mash the DNA source. Add an equal amount of water. Throw in a couple of squirts of shampoo and a spoonful of salt. Stir gently.
2. Strain the mash through a wet paper towel or cheesecloth so you're left with a clear fluid.
3. Pour an equal amount of ice-cold alcohol into the fluid. You will see a cloud form. Take a chopstick or the handle of a spoon and twirl it inside the cloud to capture long, gooey strings of nucleic acid (DNA and RNA). -Nell Boyce
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