DNA topology of highly transcribed operons in Salmonella enterica serovar Typhimurium

  • Booker B
  • Deng S
  • Higgins N
  • 38


    Mendeley users who have this article in their library.
  • 30


    Citations of this article.


Bacteria differ from eukaryotes by having the enzyme DNA gyrase, which catalyses the ATP-dependent negative supercoiling of DNA. Negative supercoils are essential for condensing chromosomes into an interwound (plectonemic) and branched structure known as the nucleoid. Topo-1 removes excess supercoiling in an ATP-independent reaction and works with gyrase to establish a topological equilibrium where supercoils move within 10 kb domains bounded by stochastic barriers along the sequence. However, transcription changes the stochastic pattern by generating supercoil diffusion barriers near the sites of gene expression. Using supercoil-dependent Tn3 and γδ resolution assays, we studied DNA topology upstream, downstream and across highly transcribed operons. Whenever two Res sites flanked efficiently transcribed genes, resolution was inhibited and the loss in recombination efficiency was proportional to transcription level. Ribosomal RNA operons have the highest transcription rates, and resolution assays at the rrnG and rrnH operons showed inhibitory levels 40-100 times those measured in low-transcription zones. Yet, immediately upstream and downstream of RNA polymerase (RNAP) initiation and termination sites, supercoiling characteristics were similar to poorly transcribed zones. We present a model that explains why RNAP blocks plectonemic supercoil movement in the transcribed track and suggests how gyrase and TopA control upstream and downstream transcription-driven supercoiling.

Get free article suggestions today

Mendeley saves you time finding and organizing research

Sign up here
Already have an account ?Sign in

Find this document


  • Betty M. Booker

  • Shuang Deng

  • N. Patrick Higgins

Cite this document

Choose a citation style from the tabs below

Save time finding and organizing research with Mendeley

Sign up for free