title: Supercoiling Effects on Short-Range DNA Looping in E. coli.
abstract: DNA-protein loops can be essential for gene regulation. The Escherichia coli lactose (lac) operon is controlled by DNA-protein loops that have been studied for decades. Here we adapt this model to test the hypothesis that negative superhelical strain facilitates the formation of short-range (6-8 DNA turns) repression loops in E. coli. The natural negative superhelicity of E. coli DNA is regulated by the interplay of gyrase and topoisomerase enzymes, adding or removing negative supercoils, respectively. Here, we measured quantitatively DNA looping in three different E. coli strains characterized by different levels of global supercoiling: wild type, gyrase mutant (gyrB226), and topoisomerase mutant (ΔtopA10). DNA looping in each strain was measured by assaying repression of the endogenous lac operon, and repression of ten reporter constructs with DNA loop sizes between 70-85 base pairs. Our data are most simply interpreted as supporting the hypothesis that negative supercoiling facilitates gene repression by small DNA-protein loops in living bacteria.
authors: Department of Biochemistry and Molecular Biology, Mayo Clinic College of Medicine, 200 First St. SW, Rochester, Minnesota 55905, United States of America.|Biochemistry and Molecular Biology track, Mayo Graduate School, Mayo Clinic College of Medicine, 200 First St. SW, Rochester, Minnesota 55905, United States of America.
authors: Lauren S
authors: LS
authors: Mogil
authors: Department of Biochemistry and Molecular Biology, Mayo Clinic College of Medicine, 200 First St. SW, Rochester, Minnesota 55905, United States of America.
authors: Nicole A
authors: NA
authors: Becker
authors: Department of Biochemistry and Molecular Biology, Mayo Clinic College of Medicine, 200 First St. SW, Rochester, Minnesota 55905, United States of America.
authors: L James
authors: LJ
authors: Maher
mesh_terms: D027081:DNA Gyrase / Q000235:genetics / Q000378:metabolism; D004264:DNA Topoisomerases, Type I / Q000235:genetics / Q000378:metabolism; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004278:DNA, Superhelical / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004587:Electrophoresis, Agar Gel; D004926:Escherichia coli / Q000235:genetics*; D017930:Genes, Reporter; D007763:Lac Operon / Q000235:genetics; D009154:Mutation; D009690:Nucleic Acid Conformation
chemical_list: D004269:DNA, Bacterial; D004278:DNA, Superhelical; D004264:DNA Topoisomerases, Type I; D027081:DNA Gyrase