Replication of duplex DNA of phage phi X174 reconstituted with purified enzymes.

Replication of the covalently closed duplex replicative form (RF) of phage phi X174 DNA has been achieved by coupling two known enzyme systems: (i) synthesis of viral strand circles (SS) from RF, and (ii) conversion of SS to nearly complete RF (RF II). In this coupled system, activated RF (gene A . RF II complex) was a more efficient template and generated as many as 10 RF II molecules per RF input, at a rate commensurate with SS synthesis. The 11 proteins required for the two component systems were all needed in the coupled RF duplication system; no new factors were required. Single-stranded DNA binding protein was needed for RF duplication at only 4% the level needed in its stoichiometric participation in SS synthesis. In addition to RF II, more complex replicative forms appeared late in the reaction, and their possible origin is discussed.