In the 1970s, Paul Berg (Stanford), Stanley Cohen (Stanford), and Herb Boyer (U.C. San Francisco) contributed to the development of DNA science by:

1. developing the "tailing" method of joining DNA fragments
    (Berg).

2. recombining joined DNA in a plasmid and maintaining it in E. coli
    using tetracycline resistance as a marker (Cohen and Chang).

3. using dual resistance to tertracycline and kanamycin resistance as dual
    indicators of transformation (Boyer).

4. producing a recombinant molecule containing genes from two
    disparate species, E. coli and the African clawed frog,
    Xenopus laevis (Cohen and Boyer).

How the Restriction Enzyme EcoRI Works: