Closer to Synthetic Life

Since the dawn of science, one of mankind's most impossible dreams has been the creation of life in a test tube.

Last week scientists moved a step closer to making the dream possible. In Palo Alto, two biochemists at the Stanford University School of Medicine reported that they had successfully synthesized a virus that could both infect bacteria and reproduce itself.

Stanford's 1959 Nobel Laureate Arthur Kornberg and Biochemist Mehran Goulian began their historic synthesis with four off-the-shelf inert chemical compounds called nucleotides--the basic building block of the DNA molecule, which controls the hereditary characteristics of every living thing. To these they added one enzyme, DNA polymerase, that is known to promote the assembly of nucleotides into the typical helix-shaped strand that characterizes the DNA molecule, and another enzyme that closes the strand into a ring.

Out with Impurities. Taking natural DNA from a simple virus called Phi X 174 (which consists only of a DNA molecule surrounded by a protein sheath), they added it to the brew as a template, or blueprint, to guide the assembly of the synthetic molecule. Under the influence of the DNA polymerase enzyme, the four basic nucleotides aligned themselves in codelike combinations alongside the natural DNA molecule. Eventually they formed a strand consisting of about 6,000 nucleotide units that was a mirror image of the corresponding strand in the natural molecule. Then, using their mirror-image molecule as a template, they repeated the process to produce a precise but synthetic duplicate of the natural DNA molecule.

Although scientists had previously accomplished this feat, the DNA molecules they produced had breaks in their strands and were not biologically active. These separations, scientists believe, were caused by enzyme impurities in the DNA polymerase. To avoid this pitfall, the Stanford team had concentrated on the complete purification of its DNA polymerase, but could not be certain that their effort had paid off without calling in expert help.

Some Day, Cancer. Separating the synthetic DNA molecules from the natural ones, the researchers sent frozen samples to Pasadena's California Institute of Technology, where Biophysicist Robert Sinsheimer tested them for biological activity.

Sinsheimer placed the synthetic DNA molecules into laboratory dishes filled with Phi X's natural victim, E. coli bacteria, which are common intestinal microbes. Invading the E. coli cells, the DNA molecules directed them to produce hundreds of Phi X viruses, each complete with its protein coat. Eventually the invaded cells ruptured under their burden of viruses, killing the bacteria and releasing the viruses to infect other cells. The progeny of the synthetic DNA molecules were not only biologically active but could not be distinguished from natural Phi X viruses.

Biochemist Kornberg, who is executive head of Stanford's biochemistry department, is no stranger to molecule synthesis. In 1959 he shared the Nobel Prize in Medicine for producing the first synthetic DNA molecule. Unlike the 1967 model, however, it was biologically inactive. He has received other awards for his work with enzymes and hopes next to learn how an enzyme like DNA polymerase actually organizes nucleotides into DNA molecules. Bio chemist Goulian worked under Korn berg as a postdoctoral fellow, and is now on the faculty of the University of Chicago Medical School. Sinsheimer is an authority on viruses, has specialized in the study of Phi X 174.

Now that active DNA has been synthesized, says Kornberg, it may be possible to alter the chemical structure of the laboratory-produced material at will.

Thus some day, he speculates, man may be able to create artificial genes to replace missing ones in persons suffering from genetic diseases. The same technique could have other far-reaching effects. The polyoma virus, which produces a variety of cancers in many animals, is almost identical in size and complexity to Phi X 174. "If one can take the polyoma DNA and modify it in the test tube by implanting alternate genes," says Kornberg, "some of these could prevent the growth of cancer cells."

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