Studies on the Joining of DNA by Polynucleotide Ligase of Phage T4

Abstract

Recently enzymes which catalyze the covalent joining of single-strand breaks in bihelical DNA have been identified and purified from Escherichia coli and phage T4- and phage T7-infected E. coli (Zimmerman et al., 1967; Olivera and Lehman, 1967a; Gefter et al., 1967; Weiss and Richardson, 1967a; Becker et al., 1967; Cozzarelli et al., 1967). We have purified polynucleotide ligase approximately 1000-fold from E. coli cells infected with bacteriophage T4 and have studied its properties (Weiss et al., 1968). The purified enzyme catalyzes the covalent joining of two segments of an interrupted strand in a DNA duplex, provided that no nucleotides are missing at the junction. Given a DNA substrate containing single-strand breaks such as those shown in Fig. 1, the enzyme catalyzes the repair by the esterification of an internally located 3′-hydroxyl group with the adjacent 5′-phosphomonoester; in the reaction ATP is cleaved to AMP and PPi.