INVIVO EFFECT OF THE TUS MUTATION ON CELL-DIVISION IN AN ESCHERICHIA-COLI STRAIN WHERE CHROMOSOME-REPLICATION IS UNDER THE CONTROL OF PLASMID-R1

The phenotypic effect of the tus::kan mutation in an Escherichia coli strain, where the chromosome is replicated unidirectionally by an integrated R1 miniplasmid, was examined by flow cytometry and phase fluorescence microscopy. The tus+ cells exhibited perturbed cell division, as indicated by the presence of many elongated cells and filaments. Inactivation of the tus gene led to a reduction in the frequency of such elongated cells, presumably by eliminating Tus-mediated polar arrests of replication forks at ter sites, thereby shortening the time required for completion of chromosome replication.