In previous studies, replicating bacteriophage T7 DNA was isolated as a rapidly sedimenting, multigenome-sized complex (100 S+ DNA), consisting of double-stranded DNA with some single-stranded regions. In the present study, 100 S+ DNA was digested with nuclease S1 and the products were fractionated by velocity sedimentation and analyzed by electron microscopy and digestion with restriction enzymes, followed by agarose gel electrophoresis. Some of the fragments released from 100 S+ DNA by nuclease S1 are linear, heterogeneous in length, and one to five times as long as mature T7 DNA. Uniformlength DNA's one, two, and four times the length of mature T7 DNA were also present in sufficiently large amounts to form visible bands during velocity sedimentation.
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