Endonuclease activity associated with purified PM2 bacteriophages.

An endonucleolytic activity is associated with purified PM(2) bacteriophages. It converts the double-stranded supercoiled PM(2) DNA mostly into the linear form that sediments as a homogenous peak in alkaline sucrose gradients. The same activity is found in intact or detergent-lysed phages. Optimal activity is observed between pH 6.8 and 7.5 at 28 degrees . Divalent cations, Mg(2+) or Mn(2+), are necessary for activity, and the enzyme is inhibited by RNA. The endonuclease has no appreciable activity on linear DNA molecules, but it attacks single-stranded circular DNA.