Abstract

Abstract Double stranded DNA serves as a template primer for Escherichia coli DNA polymerase when the DNA contains a single strand break (a nick) with a 3'-hydroxyl terminus. Initiation of replication entails covalent extension of the 3'-hydroxyl terminus and a concurrent 5' → 3' nuclease action by the enzyme. The primer strand is hydrolyzed at the 5' side of the nick while the synthetic activity catalyzes the addition of nucleotides to the 3' side. The ability of the enzyme to promote hydrolysis and synthesis simultaneously results in the translation of the nick along the DNA duplex in the 5' to 3' direction. The mechanism for conserving the 5'-strand and providing net synthesis of DNA in later phases of the reaction has not yet been clarified.