Cell‐cycle‐specific initiation of replication

SummaryThe following characteristics are relevant when replication of chromosomes and plasmids is discussed in relation to the cell cycle: the timing or replication, the selection of molecules for replication, and the coordination of multiple initiation events within a single cell cycle. Several fundamentally different methods have been used to study these processes: Meselson—Stahl density‐shift experiments, experiments with the so‐called‘baby machine', sorting of cells according to size, and flow cytometry. The evidence for precise timing and co‐ordination of chromosome replication in Escherichia coli is overwhelming. Similarly, the high‐copy‐number plasmid ColE1 and the low‐copy‐number plasmids R1/R100 without any doubt replicate randomly throughout the cell cycle. Data about the low‐copy‐number plasmids F and P1 are conflicting. This calls for new types of experiments and for a better understanding of how these plasmids control their replication and partitioning.