Isolation and characterisation of a strain carrying a conditional lethal mutation in the cou gene of Escherichia coli K12

Abstract

A strain which carries a mutation conferring clorobiocin resistance and temperature sensitivity for growth was isolated from Escherichia coli K12. Genetic mapping and the molecular weight of the gene product suggest that the mutation is in the cou gene, specifying a sub-unit of DNA gyrase. Nuclear organisation and segregation and placement of septa are grossly abnormal in the mutant at 42 degrees C. RNA synthesis and initiation of DNA replication are also affected at the restrictive temperature but the rate of DNA chain elongation continues almost undisturbed.

DNA Gyrase Is Involved in Chloroplast Nucleoid Partitioning

“…Similar phenotypes are observed in the gyrase mutants of E. coli, where the inhibition of gyrase leads to a 3.5-fold increase in the percentage of nucleoids possessing a doublet morphology (Steck and Drlica, 1984). Furthermore, elongated cells of an E. coli gyrase mutant bud off DNA-less minicells, indicating that unsegregated chromosomes may block normal division and force the cells to use secondary division sites (Orr et al, 1979). More recently, it has been revealed that the nucleoid indeed negatively regulates cell division by preventing the formation of the FtsZ ring (Margolin, 2001).…”

Confocal scanning light microscopy of Escherichia coli nucleoid: Comparison with phase contrast and electron microscope images

“…We have studied this problem also with the gyrase B mutant. Inhibition of gyrase B does not prevent cell elongation, and the nucleoid becomes centrally located in the cell (13). Figures lb, c, and d show the increase in detail obtained by CSLM as compared with the phase-contrast LM image (Fig.…”

“…42°C leads to the formation of two types of cells: large, DNA-containing filaments and small, DNA-less cells (13).…”

Topoisomerase I mutants: the gene on pBR322 that encodes resistance to tetracycline affects plasmid DNA supercoiling.

“…DNA gyrase is an essential enzyme in bacteria: conditional lethal mutations have been obtained in the genes encoding gyrase subunits (17)(18)(19), and gyrase is the target of two classes of antibiotic (11,20,21). In contrast, topoisomerase I is not essential: deletion mutants are viable (22).…”