1. developing the "tailing" method of joining
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: