On the Mechanism of the Polynucleotide Joining Reaction

Polynucleotide-joining enzymes (ligases) have been identified in uninfected and phage-infected Escherichia coli (Gellert, 1967; Olivera and Lehman, 1967a; Zimmerman et al., 1967; Gefter et al., 1967; Weiss and Richardson, 1967a; Cozzarelli et al., 1967). Both types of enzyme catalyze the synthesis of a phosphodiester bond between the 3′ hydroxyl and 5′ phosphoryl termini of DNA chains which have been properly aligned in a double-helical structure. Such enzymes are of interest because of their possible involvement in genetic recombination, ‘dark’ repair of ultraviolet-induced lesions, and in DNA synthesis. It has already been demonstrated that the polynucleotide ligase induced by phage T4 is essential for normal T4 DNA replication (Fareed and Richardson, 1967).