Cohen and Boyer recombinant DNA cloning

In 1972 researchers including Herbert Boyer, a biochemist at the University of California, San Francisco, realized that the restriction enzyme EcoRI, found in his laboratory, left staggered ends on the DNA it cut. Any two pieces cut by it had matching ends that could latch together with no further chemistry. Boyer and Robert Helling first tried to use it on the DNA of the bacterial virus lambda, but the enzyme cut that DNA in five places instead of one.

In November 1972 Boyer and Stanley Cohen of Stanford University were both in Hawaii for a joint US and Japanese meeting on plasmids, the small rings of DNA that bacteria carry apart from their chromosome. Boyer spoke about the ends EcoRI produced. Cohen described a procedure from his laboratory that let bacteria take up plasmid DNA and pass identical, self-copying plasmids to their offspring. Over sandwiches late one night they planned to work together.

The first success came in spring 1973 with one of Cohen's plasmids, pSC101, which made E. coli resistant to tetracycline and which EcoRI cut at a single site without destroying its ability to replicate. Mixed with other DNA cut by the same enzyme, the opened rings joined with the new fragments into fresh loops. Another enzyme sealed the remaining nicks, the loops went into calcium chloride-treated bacteria, and only bacteria carrying the recombinant plasmids survived on tetracycline plates. The team then joined tetracycline-resistance and kanamycin-resistance plasmids. Their paper in the Proceedings of the National Academy of Sciences, with A. C. Chang and Helling, appeared in November 1973.

Next they moved DNA across species: a plasmid piece from Staphylococcus was spliced into an E. coli plasmid and propagated in E. coli. In the summer of 1973 John Morrow, a graduate student in Paul Berg's laboratory, worked with Cohen and Boyer to put genes of the South African clawed frog into E. coli. The same year, worry about the hazards of such work led to the first Asilomar conference on biohazards. In 1976 Boyer and the venture capitalist Robert Swanson founded Genentech to turn the technique into products.