Replication of phage G4. A novel and simple system for the initiation of deoxyribonucleic acid synthesis.

Conversion in vitro of single-stranded circular DNA of phage G4 (related to phage phiX174) to the double-stranded replicative form (RF-II) depends on a novel and relatively simple group of three proteins: a priming protein of approximately 65,000 daltons, the DNA unwinding protein, and the DNA polymerase III holoenzyme. Stimulation by ATP and GTP suggests an RNA synthetic step in the priming of DNA synthesis. The synthetic strand in the RF-II contains a small gap at a unique position relative to the template strand; the 5' end of the gap is about 250 nucleotide residues (5% of the genome length) away from the single site of cleavage by a restriction endonuclease (Eco RI).