Modulation of HU-DNA interactions by salt concentration and applied force

Botao Xiao*, Reid C. Johnson, John F. Marko

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

55 Scopus citations

Abstract

HU is one of the most abundant proteins in bacterial chromosomes and participates in nucleoid compaction and gene regulation. We report experiments using DNA stretching that study the dependence of DNA condensation by HU on force, salt and HU concentration. Previous experiments at subphysiological salt levels revealed that low concentrations of HU could compact DNA, whereas larger HU concentrations formed a DNA-stiffening complex. Here we report that this bimodal binding behavior depends sensitively on salt concentration. Only the compaction mode was observed for 150 mM and higher NaCl levels, i.e. for physiological salt concentrations. Similar results were obtained for the more physiological salt K-glutamate. Real-time studies of dissociation kinetics revealed that HU unbound slowly (minutes to hours under the conditions studied) but completely for salt concentrations at or above 100 mM NaCl; the lifetime of HU complexes was observed to increase with the HU concentration at which the complexes were formed, and to decrease with salt concentration. Higher salt levels of 300 mM NaCl completely eliminated observable HU binding to DNA. Finally, we observed that the dissociation kinetics depend on force applied to the DNA: increased applied force in the sub-piconewton range accelerates dissociation, suggesting a mechanism for DNA tension to regulate chromosome structure and gene expression.

Original languageEnglish (US)
Article numbergkq435
Pages (from-to)6176-6185
Number of pages10
JournalNucleic acids research
Volume38
Issue number18
DOIs
StatePublished - May 22 2010

ASJC Scopus subject areas

  • Genetics

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