Replication of mini-F plasmid in vitro promoted by purified E protein.

An in vitro system for replication of mini-F plasmid DNA was constructed. This system consists of an ammonium sulfate fraction II (Fuller et al. 1981) from Escherichia coli extract, exogenously added purified E protein encoded by mini-F plasmid, and mini-F DNA in a closed circular form. Experiments with this system showed that the 217 bp DNA region which contains the A + T rich cluster and the four 19 bp direct repeats responsible for incB incompatibility is essential for mini-F DNA replication.