INHIBITION AND RESTART OF INITIATION OF CHROMOSOME-REPLICATION - EFFECTS ON EXPONENTIALLY GROWING ESCHERICHIA-COLI-CELLS

Escherichia coli strains in which initiation of chromosome replication could be specifically blocked while other cellular processes continue d uninhibited mere constructed. Inhibition of replication resulted in a reduced growth rate and in inhibition of cell division after a time period roughly corresponding to the sum of the lengths of the C and D periods. The division inhibition was not mediated by the SOS regulon. The cells became elongated, and a majority contained a centrally locat ed nucleoid with a fully replicated chromosome. The replication block was reversible, and restart of chromosome replication allowed cell div ision and rapid growth to resume after a time delay. After the resumpt ion, the septum positions were nonrandomly distributed along the lengt h aids of the cells, and a majority of the divisions resulted in at le ast one newborn cell of normal size and DNA content. With a transient temperature shift, a single synchronous round of chromosome replicatio n and cell division could be induced in the population, making the con structed system useful for studies of cell cycle-specific events. The coordination between chromosome replication, nucleoid segregation, and cell division in E. coli is discussed.