A circular form of bacteriophage P1 DNA made in lytically infected cells of Escherichia coli Characterization and kinetics of formation

Covalently closed circular (CCC) DNA molecules are formed in Escherichia coli following lytic infection with phage P1. These molecules appear to be identical in size to the circular species present in P1 lysogens. Kinetic studies on the formation of CCC DNA show newly synthesized CCC DNA is first detected at 7 min after infection and that its rate of synthesis increases to a maximum value at 30 min, about midway through the infection cycle. Subsequently, the rate of synthesis drops rapidly although CCC DNA is present till late in infection. A conservative estimate indicates that 8% or more of the newly synthesized P1 DNA made at 30 min after infection can be converted to a closed circular form.