DNA encodes the information for all the proteins inside the cell, their amino acid sequence, when and where to turn them on, and a whole lot of other things that we probably dont fully understand yet. With the ability to write DNA, to synthesize our own arbitrary stretches of As, Ts, Cs, and Gs, we can create our own instructions for cellular proteins or we can encode sequences that would be junk to a cell but that we could read as a message. This week, George Church, Yuan Gao, and Sri Kosuri published a short paper demonstrating that not only could we encode a few phrases here and there, but write a whole book in DNA. The book, Churchs Regenesis: How Synthetic Biology Will Reinvent Nature and Ourselves, which will be published using more traditional means this fall, includes 53,426 words, 11 jpgs, and one JavaScript program. The text and images were converted to html format and then read as bits, 1s and 0s that can be easily encoded into DNA: A or C for 0 and T or G for 1. Having two possible letters for each bit means that the sequence wont end up with long stretches of any single letter, a challenge for chemical DNA synthesis. The perl code they used to covert bits to DNA is available in the papers supplementary information (PDF).
This is by far the largest amount of non-biological information synthesized and stored in DNAa total of 5.27 megabits, way beyond the 7,920 bit record previously held by the Venter Institutes watermarks in their chemically synthesized genome (written using an undisclosed code for each letter and punctuation mark).
The sequence of Watermark 4 in the Venter Institute's synthetic genome
While news reports about the DNA book often acknowledge this previous DNA message, as well as a 1999 paper encoding the World War II spy message JUNE 6 INVASION: NORMANDY in DNA (PDF), they dont mention the very first synthetic DNA message cited in the paper. In 1988, Joe Davis, an artist collaborating with molecular biologist Dana Boyd in Jon Beckwiths lab at Harvard Medical School (and currently a research affiliate in George Churchs lab), designed and synthesized an 18 base-pair message encoding the image of the ancient Germanic rune representing life and the female earth. The Microvenus message was then pasted into a vector and transformed into E. coli, creating a living work of art.
Microvenus--The first non-biological message encoded in DNA, by Joe Davis
The Arecibo Message
The coding scheme for Microvenus was inspired by the binary message sent by Carl Sagan and Frank Drake from the Arecibo radio telescope in 1974, an attempt to open up communication with extraterrestrial intelligence (as well as demonstrate the capabilities of the newly remodeled telescope). The image is a 2373 rectangle (having the dimensions be two prime numbers makes it easier to decode the single stream of binary digits) showing pictures of the telescope, a person, and information about our solar system and our DNA. Microvenus is coded with a similar principle, the lines of the image translated to ones and zeros in a 57 grid, converted to DNA with phase-change values rather than numerical values. The DNA bases are arranged by size C= 1, T=2, A =3, G=4 and represent the number of bits needed before you switch to the opposite bit. For example, 10101 translates to CCCCC because each digit occurs once before it switches, and 00011 would be AG because there are three 0 before it switches to two ones.
Despite its tendency to mutate and evolve as cells divide, DNA is a remarkably inert and stable chemical on its own, lasting long enough for archeologists to be able to sequence strands of DNA many thousands of years old. In a microbial spore hurtling through space, DNA could theoretically last long enough to be found by an extraterrestrial civilization that could sequence it and decode the message inside. In the late 1970s, some scientists even hypothesized the inverse possibilitythat viruses on Earth could have been sent as messages from extraterrestrials. Attempts to decode the X174 viral genome sequence into two dimensional images of course didnt yield any striking alien messages, but did open up the possibility of sending out different kinds of messages of our own.
For Davis, the messages that we send to aliens arent just about sending out a friendly description of life, art, and science on Earth, but of better understanding those things ourselves. He writes in his paper describing the Microvenus project:
By sending messages to extraterrestrial intelligence, human beings are importantly engaged in a search for themselves. They must first reveal themselves to themselves before they can reveal themselves to anyone else. This has not only been a central dilemmain the search for extraterrestrial intelligence, but it has also been an essential element of art, history, psychology, and classical philosophy.
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Communicating with Aliens through DNA
