Synthesis of phiX174 viral DNA in vitro depends on phiX replicative form DNA.

A cell-free system that catalyzes phiX174 replicative form I (supercoiled circular duplex, RFI)-dependent phiX174 DNA synthesis has been isolated from Escherichia coli infected with phiX174 phage. The products formed with such preparations are viral strands as judged by hybridization to poly(U,G) followed by equilibrium centrifugation in CsCl. This phiX174 DNA-synthesizing involves formation of DNA-protein complexes that sediment in neutral sucrose with S values of 50, 60-70, and higher. The 50S complex contained a rolling-circle replicative intermediate DNA with an extended tail of single-stranded viral DNA. The DNA contained in the 60-70S region was a mixture of circular and linear single-stranded DNA, RFI, and RFII with an extended single-stranded tail. Such complexes have been isolated during in vivo progeny phiX174 DNA synthesis [Fujisawa, H. & Hayashi, M. (1976) J. Vriol. 19,409]. In vitro, maximal phiX174 DNA synthesis was shown to require the genetically defined proteins E. coli dna B, dna C, dna G, dna Z, rep. phiX174 gene A product, and other phiX174 coded proteins. The synthesis of phiX174 DNA is ATP-dependent and is inhibited by nalidixic acid and novobiocin but is resistant to rifampicin.