Initiation of lambda DNA replication in vitro promoted by isolated P-gene product [Escherichia coli]

The product of the P gene of bacteriophage lambda was isolated from heat‐induced λ‐lysogenic Escherichia coli cells. It was found to bind to DNA, to be devoid of nuclease activity acting on double‐stranded λ DNA and of nicking/closing activity. Initiation of λ DNA replication promoted by the P‐gene product in a complementation assay in vitro was sensitive to rifampicin. Sedimentation analysis of the products and their hybridization to separated λ DNA strands indicate that λ DNA was formed in a reaction similar to ring‐to‐ring replication in vivo. The reaction was symmetric from the beginning, i.e. both λ DNA strands were copied without delay.