Replication of the ampicillin resistance plasmid RSF1030 in extracts of Escherichia coli: separation of the replication cycle into early and late stages.

The replication cycle of the small resistance plasmid RSF1030 can be divided into two stages with different enzyme requirements: (1) Synthesis of early replicative intermediates containing 7 S DNA catalyzed by DNA polymerase I in the absence of functional dnaZ protein, and (2) replication of early intermediates requiring DNA polymerase III holenzyme (including the dnaZ protein). Early intermediate DNA synthesized in a dnaZ extract can be converted to fully replicated plasmid molecules upon addition to a replication enzyme fraction prepared by ammonium sulfate fractionation of polA I extracts. The first-stage reaction is sensitive to rifampicin, novobiocin, and oxolinic acid, but insensitive to arabinosylcytosine triphosphate (aCTP). Addition of aCTP interferes with the second-stage reaction resulting in the accumulation of late replicative intermediates.