An enzyme system for replication of duplex circular DNA: the replicative form of phage phi X174.

Viral single strands (SS) are converted to the duplex from (RF) by a soluble enzyme fraction uninfected Escherichia coli [Schekman et al. (1975) J. Biol. Chem. 250, 5859-5865]. When reactions were supplemented with a soluble enzyme fraction from phi X174-infected cells, replication of phi X174 superhelical RF I DNA was observed. The activity supplied by infected cells was absent in cells treated with chloramphenicol or in cells infected with a phi X174 phage mutant in cistron A (cis A). A host function coded by the rep gene, essential in vivo for RF replication (but not for SS leads to RF), was supplied by enzyme fractions from either infected or uninfected cells. Based on complementation assays, the cisA-dependent and the rep-dependent proteins have each been purified about 1000-fold. The synthetic products of the enzymatic reaction were identified as RF I and RF II in which viral (+) and complementary (-) strands were newly synthesized.