Studies on T4-induced Nucleases

A nuclease has been isolated from T4-infected Escherichia coli which attacks single- or double-stranded DNA from a variety of sources, including T4. The enzyme appears late during the T4 development, and its action is dependent on the presence of —SH reagents and Mg++ or Mn++ ions. The rate and extent of the reaction on single-stranded DNA is about 10-fold higher in the presence of Mn++ than in the presence of Mg++. Single and double-strand breakage of native DNA was observed in reaction mixtures containing Mn++ while no reaction with native DNA was detected in the presence of Mg++. The products of the enzymatic reaction include oligonucleotides which contain 3'-OH and 5'-phosphate ends. While all four nucleotides are found at the 5' end, a preference toward A and T was noted. T4 mutants in genes 49, 16, or 17 which lead to defects in phage maturation induce wild type levels of the nuclease. In contrast, T4 mutants in gene 43 (T4 DNA polymerase) do not induce late functions and for this reason do not induce the Mn++-activated nuclease.