Evidence for polarity of chromosome replication in F−strains ofEscherichia coli

Abstract

The inducibility of three enzymes (β-galactosidase, tryptophanase and D-serine deaminase) has been measured at various times during the cell cycles of three strains ofEscherichia coli(K12 58–161 F⁻, B/r F^–and 15T⁻). In each strain sharp increases in inducibility of these enzymes occurred at characteristic periods in each cell cycle. Such increases depend on DNA replication and therefore probably reflect synchronized gene replication. It is inferred that chromosome replication in these F⁻strains is sequential from a fixed origin.Infection with F′Lack⁺results in an extra period of increase in inducibiity of β-galactosidase in each cell cycle. It is concluded that the F′ episome replicates once in each cell cycle at a time soon after cell separation.