Friday, September 5, 2008

This Week's Citation Classic: Genetic Engineering

Genetic engineering is ubiquitous in biology labs today, and a popular whipping boy among a society that little recognizes the benefits it provides. But where did it all begin?

Over hot pastrami sandwiches in Waikiki.

This week's citation classic is: Cohen SN, Chang ACY, Boyer HW and Helling RB. 1973. Construction of Biologically Functional Bacterial Plasmids In Vitro. PNAS USA 70: 3240-3244.

In 1972, Herb Boyer, a biochemist at the University of California at San Francisco, and Stan Cohen, an associate professor of medicine at Stanford University, were presenting at a conference on bacterial plasmids in Hawaii when they noticed the complementary nature of their work. Following the conference, they met at a deli to hash out the details of the following experiment.

Cohen had previously determined how to make E. coli take in foreign DNA (a citation classic worthy feat in itself) when he transformed E. coli with a plasmid known as pSC101, that conferred resistance to the antibiotic tetracycline.

Boyer on the other hand had discovered EcoRI, a restriction enzyme that could snip open pSC101 while leaving "sticky ends".

Like chocolate and peanut butter, the combination was unbeatable. Cohen and Boyer realized they could combine their techniques to create a new plasmid containing foreign DNA.

First they digested the African clawed toad, Xenopus laevis, DNA with EcoRI to isolate the rRNA gene. Then they cleaved pSC101 with EcoRI. Since pSC101 has only a single restriction site, the plasmid was linearized. Because of the sticky ends, the plasmid and the Xenopus DNA joined together when placed in the same test tube, thus creating a recombinant plasmid. Using Cohen's technique, the plasmid containing the foreign DNA could then be transformed into E. coli where it would now be expressed. Genetic engineering was born!


  1. Because of the sticky ends, the plasmid and the Xenopus DNA joined together when placed in the same test tube...
    Whaaa...? No ligase?

    You forgot to mention that Boyer proceeded to call up a venture capitalist, started a little company called Genentech, and made a gazillion dollars. So much money, in fact, that they won't give him a Nobel Prize. Now he's filthy rich and embittered.

  2. Well there are a number of things I didn't mention such as ligase and the fact that Boyer and Cohen patented the technology. Editorial judgement!