1. Isolation of a DNA fragment containing a gene of interest that needs to be cloned (called as insert).
2. Generation of a recombinant DNA (rDNA) molecule by insertion of the DNA fragment into a carrier DNAmolecule called vector (e.g. plasmid) that can self replicate within a host cell.
3. Transfer of the rDNAinto an E. coli host cell (process called transformation).
4. Selection of only those host cells carrying the rDNA and allowing them to multiply thereby multiplying the rDNA molecules.
Paul Berg, Herbert Boyer, Annie Chang and Stanley Cohen.