Process of Attachment of 0X174 Parental DNA to the Host

The 0X174-DNA membrane complex was isolated from Escherichia co//infected with 0X174 am3 by isopycnic sucrose gradient centrifugation followed by zone electrophoresis. The 0X174 DNA-membrane complex banded at two positions, intermediate density membrane fraction and cytoplasmic membrane fraction, having buoyant densities of 1.195 and 1.150 g/ml, respectively. Immediately after infection with 0X147, replicating DNA was pulse-labeled and then the incorporated label was chased. The radioactivity initially recovered in the intermediate density membrane fraction migrated to the cytoplasmic membrane fraction. The DNAs from both complexes sedimented mainly at the position of parental replicative form I (RFI). The 0X174 DNA-membrane complex contained a specific membrane-bound protein having a molecular weight of 80,000 which is accumulated in the host DNA-membrane complex. These results suggest that when 0X174 DNA penetrated into cells in the early phase of infection, single-stranded circular DNA was converted to parental RFI at a wall/ membrane adhesion region and migrated to the cytoplasmic membrane fraction, where the parental RF could serve as a template in the replication of progeny RF. The association of parental DNA of bacteriophage 0X174 with a host cell component was first demon-strated in 1968 by Knippers and Sinsheimer (/). They showed by sucrose gradient centrifugation that the parental DNA is recovered in a fast sedimenting host cell component fraction after the phage DNA penetrates into host cells. The mem-brane-like properties of this fast sedimenting com-ponent were described by several investigations (2-4). Recently, Jazwinski et al. reported tha