Terminal Cross-linking of DNA Catalyzed by an Enzyme System Containing DNA Ligase, DNA Polymerase, and Exonuclease of Bacteriophage T7

Abstract

An enzymatic activity that terminally cross-links T7 DNA has been detected in extracts from phage T7-infected Escherichia coli cells. This activity required the functional products of gene 1.3 (T7 DNA ligase), gene 5 (T7 DNA polymerase), and gene 6 (T7 exonuclease) as well as Mg²⁺ ions, the four deoxytriphosphates, and ATP. The cross-linking system could be reconstituted with purified ligase, polymerase, and exonuclease, and maximal activity required the presence of all three enzymes. The system was active on phage DNA which possessed unique termini but not on DNA with non-unique ends.