Enzymatic reactions at termini of DNA

A number of reactions which lead to the removal of 3′-phosphate and 5′-phosphate ends of DNA have been detected in extracts of E. coli. Two new enzymes which attack the ends of DNA chains have been purified from phage-infected cells. One enzyme removes only 3′-phosphate termini specifically from DNA, whereas the other removes only 5′-phosphate ends from both DNA and RNA. Synthetic reactions occurring at ends of DNA have also been detected. In phage-infected extracts, 5′-hydroxyl polynucleotide kinase catalyzes the phosphorylation of 5′-hydroxyl-terminated polynucleotides. Another phage-induced enzyme, in the presence of ATP and deoxynucleoside triphosphates, leads to the conversion of 5′-32P-labeled DNA to a form resistant to alkaline phosphatase. This enzyme preparation also catalyzes the conversion of the Hershey circle form of lambda DNA to a covalent form. Enzyme fractions purified from E. coli K12 also catalyze the latter reaction.