Science: A genetic code for secrets

Strands of DNA have provided the next breakthrough for espionage.

SPYING MAY become a genetic activity, now that scientists have for the first time written a secret wartime message into the chemical code of a DNA molecule. The ability to write a simple English-language message in the biological alphabet of the genes could herald a host of as-yet-undiscovered uses for this encryption technique.

Scientists from the Mount Sinai School of Medicine in New York attempted the feat after reading an article in a 1946 copy of the Reader's Digest, written by the legendary J Edgar Hoover, then director of the Federal Bureau of Investigation (FBI). Hoover explained how the discovery of microdots - the secret messages miniaturised on to dots of microfilm that can be stuck on to a full stop in an otherwise innocuous letter - proved to be a crucial breakthrough in the war against Nazi espionage.

The FBI discovered the first microdot after interrogating the playboy son of a well-known Balkan millionaire, who was a suspected Nazi sympathiser. FBI investigators examined with scrupulous care every item the Balkan was carrying. An envelope scrutinised carefully under a slanted light revealed a tiny gleam. "A dot had reflected the light," Hoover wrote. "A dot - a punctuated period on the front of the envelope; a black particle no bigger than a fly speck."

Under a microscope, the dot turned out to be a tiny version of a typewritten text of instructions on how the spy should gather evidence of America's "atomic-kernel energy" and uranium shipments. "Now we had it! The German espionage service had found a way to photograph a full-sized letter down to the size of a midge," Hoover wrote.

Now the Mount Sinai scientists - Professor Carter Bancroft, Catherine Taylor Clelland and Viviana Risca - have adapted the microdot method to DNA. "Our technique is based upon the concept of `steganography', which dates from 1499 and literally means `covered writing'. Steganography basically involves putting a secret message into a form such that it can be concealed by hiding it among a large number of objects to which it is physically similar," Professor Bancroft says.

The researchers synthesised a short stretch of DNA with the wartime message "June 6 Invasion: Normandy" encrypted into a sequence of chemicals that normally form the genetic information of the molecule. Each letter of the English alphabet was ascribed a certain triplet sequence of three out of the four DNA chemicals that make the genetic code. They even incorporated the synthetic DNA message as a "microdot" and stuck it on to a full stop in a letter to show that the information can be deciphered after being sent through the post.

Short messages encoded in a synthetic stretch of DNA by converting the English alphabet into the genetic code are easily concealed in the vast background of information that makes up the full complement of a living organism's DNA, Professor Bancroft says. He likens the concealment to incorporating a thread into a carpet made up of 30 million threads of DNA. "Such a carpet would present an exceedingly rich and complex tapestry."

Extracting the DNA message from the background information is done by incorporating a recognisable code at the beginning of the message which acts like a "hook" to enable someone with the code to pull out the right thread from the surrounding tapestry. Professor Bancroft believes the technique could prove to be more than of purely academic interest. "There will be benefits we just haven't thought of yet," he says. He preferred, however, not to comment on whether any intelligence agencies have taken an interest in his invention, reported in Nature.