title: A biomechanical mechanism for initiating DNA packaging.
abstract: The bacterial chromosome is under varying levels of mechanical stress due to a high degree of crowding and dynamic protein-DNA interactions experienced within the nucleoid. DNA tension is difficult to measure in cells and its functional significance remains unclear although in vitro experiments have implicated a range of biomechanical phenomena. Using single-molecule tools, we have uncovered a novel protein-DNA interaction that responds to fluctuations in mechanical tension by condensing DNA. We combined tethered particle motion (TPM) and optical tweezers experiments to probe the effects of tension on DNA in the presence of the Hha/H-NS complex. The nucleoid structuring protein H-NS is a key regulator of DNA condensation and gene expression in enterobacteria and its activity in vivo is affected by the accessory factor Hha. We find that tension, induced by optical tweezers, causes the rapid compaction of DNA in the presence of the Hha/H-NS complex, but not in the presence of H-NS alone. Our results imply that H-NS requires Hha to condense bacterial DNA and that this condensation could be triggered by the level of mechanical tension experienced along different regions of the chromosome.
authors.affiliation: Department of Chemical and Physical Sciences, University of Toronto Mississauga, Mississauga, ON L5L 1C6, Canada.
authors.forename: Haowei
authors.initials: H
authors.lastname: Wang
authors.affiliation: Department of Chemical and Physical Sciences, University of Toronto Mississauga, Mississauga, ON L5L 1C6, Canada Department of Physics, University of Toronto, Toronto, ON M5S 1A7, Canada.
authors.forename: Samuel
authors.initials: S
authors.lastname: Yehoshua
authors.affiliation: Department of Molecular Genetics, University of Toronto, Toronto, ON M5S 1A8, Canada.
authors.forename: Sabrina S
authors.initials: SS
authors.lastname: Ali
authors.affiliation: Department of Molecular Genetics, University of Toronto, Toronto, ON M5S 1A8, Canada.
authors.forename: William Wiley
authors.initials: WW
authors.lastname: Navarre
authors.affiliation: Department of Chemical and Physical Sciences, University of Toronto Mississauga, Mississauga, ON L5L 1C6, Canada Department of Physics, University of Toronto, Toronto, ON M5S 1A7, Canada josh.milstein@utoronto.ca.
authors.forename: Joshua N
authors.initials: JN
authors.lastname: Milstein
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001696:Biomechanical Phenomena; D042003:DNA Packaging; D004269:DNA, Bacterial / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D009154:Mutation
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; C031908:H-NS protein, bacteria