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Highly concerned about the uncertainties of infecting laboratory bacteria similar to those in man with known cancer genes. Pollack immediately called Stanford and raised his doubts. The experimenter, Biochemist Paul Berg, listened politely but saw no reason for alarm. He knew that SV40 had been handled without ill effects by countless laboratory workers and had even been inadvertently included in some of the first batches of oral polio vaccine without doing any apparent harm. Indeed, Berg felt that the experiment was not only safe but extremely important. SV40's appeal lies in the fact that it has only a few genes, one of which apparently has the ability to turn normal cells into cancerous ones. If anyone could unlock the mysteries of this lethal gene—a goal of laboratories around the world (and the kind of discovery that might well win a Nobel Prize) —he would have taken a major step toward understanding the elusive mechanism of cancer.
When Berg asked his colleagues about the experiment, some of them also expressed misgivings. What if an altered E. coli, carrying SV40 genes, planted a slow-ticking cancer time bomb in the human gut? Nagged by such questions, Berg canceled his experiment. But even while Berg was agonizing over the decision, scientists made two dramatic discoveries that would vastly simplify recombinant work.
At the University of California at San Francisco, Herbert Boyer and his colleagues found an exceptional new cutting enzyme. Unlike available restriction enzymes, it did not break apart the twin-stranded DNA with a simple slice. Instead, it caused an overlapping, mortise-type break that automatically left a bit of '"sticky" single-stranded DNA at each end, to which new mate rial could be readily attached. Previously, Berg and others who worked in the field had to create such sticky tails synthetically.
The other breakthrough came when Stanley Cohen and his team, working in a Stanford lab two floors below Berg's, found a remarkable plasmid, which was promptly dubbed pSC (Cohen's initials) 101. It had the uncanny ability to take on a new gene and to slip into E. coli. Word of Cohen's miraculous little gene conveyor spread rapidly, and experimenters from all over the world besieged him for samples. Usually, scientists are more than willing to oblige such requests. But because pSC 101. in conjunction with Boyer's new enzymatic scalpel, made the creation of novel gene combinations so easy, Cohen was hesitant about distributing the material.