Abstract
Site-specific genetic recombinations promoted in vivo by the EcoRI endonuclease has been demonstrated by using constructed hybrid plasmids in which the chloramphenicol resistance gene was inactivated by insertion of DNA fragments at an EcoRI site within the gene. Such recombination can involve either the joining of intracellularly generated cohesive termini of the same DNA fragment or intermolecular ligation of different DNA fragments. DNA cleavage and ligation in vivo are precise: recombinant DNA molecules show functional continuity of the gene sequence cleaved by the enzyme and regeneration of nucleotide recognition sites for both the EcoRI endonuclease and the EcoRI DNA methylase. In other experiments, EcoRI-generated fragments of eukaryotic DNA that had not been modified by the Escherichia coli K methylase were shown to be taken up by bacterial cells and to undergo intracellular ligation to segments of bacterial plasmid DNA.