Properties of membrane-associated folded chromosomes of E. coli related to initiation and termination of DNA replication

Analysis of folded chromosomes prepared from amino acid-starved E. coli cells or from a dnaC initiation mutant indicates that a unique structure is associated with completion or near completion of rounds of chromosome replication in E. coli. Chromosomes remain associated with portions of the bacterial cell envelope throughout the DNA replication cycle, but become more rapidly sedimenting as replication proceeds in the absence of reinitiation. Before reinitiation of chromosome replication occurs after restoring required amino acids to amino acid-starved cells or after lowering the temperature in a thermosensitive dnaC mutant, sedimentation velocities of the membrane-associated folded chromosomes decrease substantially. The decrease in sedimentation velocity does not depend on renewed DNA synthesis, but does require the activity of at least the dnaC gene product.