摘要：

Four discrete species of DNA that appear after the infection of a sensitive strain of Escherichia coli K12 with temperate phage Mu1 have been identified by neutral and alkaline sucrose gradient centrifugation, CsCl-ethidium bromide equilibrium gradient centrifugation, electron microscopy, differential labeling and DNA-DNA hybridization. Form I (32S) resembles the DNA extracted from phage particles. Form II is also linear but sediments faster (39 S). Form II (46 S) is a relaxed ring form with and without "tails." Form IV (55 S and faster) consists of covalently closed superhelical rings. Forms III and IV exhibit a continuous range of weights between 25 and 134 × 10 6 daltons. All forms contain host DNA. Excision of DNA of the length of phage DNA from an intermediate made of alternating segments of host and phage DNA is proposed to account for the generation of phage DNA molecules containing host DNA at their "variable end," and for the formation of the generalized transducing DNA found in Mu particles.

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