title: Native supercoiling of DNA: the effects of DNA gyrase and omega protein in E. coli.
abstract: This study deals with the effects of a temperature-sensitive (ts) mutation at the gene encoding the DNA gyrase B subunit (gyrBts) and a deletion of the top gene encoding the omega protein upon the superhelical density of the pAO3 plasmid in E. coli cells. The alteration of the DNA gyrase B subunit is shown to lead to a partial relaxation of DNA. On the other hand, the lack of omega protein due to the top gene deletion leads to an abnormally high degree of DNA supercoiling. In a double gyrBts delta top mutant the DNA supercoiling is greater than native at the permissive temperature, while under nonpermissive conditions a partial relaxation is observed. However, the pattern of DNA relaxation in the latter case is quite different from that in a single gyrBts mutant. The conclusion is that the native supercoiling of DNA in the cell is maintained through the counter-activities of DNA gyrase and the omega protein.
mesh_terms: D004264:DNA Topoisomerases, Type I / Q000235:genetics*; D004250:DNA Topoisomerases, Type II / Q000235:genetics*; D004278:DNA, Superhelical / Q000235:genetics*; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics*; D005796:Genes; D005798:Genes, Bacterial; D005838:Genotype; D009154:Mutation; D010957:Plasmids
chemical_list: D004278:DNA, Superhelical; D004264:DNA Topoisomerases, Type I; D004250:DNA Topoisomerases, Type II