Open AccessSupercoiling Effects on Short-Range DNA Looping in E. coli
Author(s) -
Lauren S. Mogil,
Nicole A. Becker,
Jim Maher
Publication year - 2016
Publication title -
plos one
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.99
H-Index - 332
ISSN - 1932-6203
DOI - 10.1371/journal.pone.0165306
Subject(s) - dna supercoil , dna gyrase , lac repressor , dna , topoisomerase , biology , operon , mutant , escherichia coli , nucleoid , psychological repression , microbiology and biotechnology , circular bacterial chromosome , lac operon , base pair , plasmid , gene , genetics , biophysics , gene expression , dna replication
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.