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The gene A product of Escherichia coli bacteriophage varphiX 174, necessary for initiation of varphiX DNA synthesis, has been identified and purified to near homogeneity. The gene A protein is shown to be a highly specific DNA endonuclease which breaks one phosphodiester bond in the viral strand of either double-stranded, circular varphiX replicative form I (RFI), or in single-stranded, circular varphiX viral DNA; it is inactive against all other species of DNA tested.
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Henry et al. (1974) studied this question.
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