title: DNA Twist Stability Changes with Magnesium(2+) Concentration.
abstract: To understand DNA elasticity at high forces (F>30  pN), its helical nature must be taken into account, as a coupling between twist and stretch. The prevailing model, the wormlike chain, was previously extended to include this twist-stretch coupling. Motivated by DNA's charged nature, and the known effects of ionic charges on its elasticity, we set out to systematically measure the impact of buffer ionic conditions on twist-stretch coupling. After developing a robust fitting approach, we show, using our new data set, that DNA's helical twist is stabilized at high concentrations of the magnesium divalent cation. DNA's persistence length and stretch modulus are, on the other hand, relatively insensitive to the applied range of ionic strengths.
authors.affiliation: LaserLaB Amsterdam and Department of Physics and Astronomy VU University Amsterdam, 1081 HV Amsterdam, Netherlands.
authors.forename: Onno D
authors.initials: OD
authors.lastname: Broekmans
authors.affiliation: LaserLaB Amsterdam and Department of Physics and Astronomy VU University Amsterdam, 1081 HV Amsterdam, Netherlands.
authors.forename: Graeme A
authors.initials: GA
authors.lastname: King
authors.affiliation: LaserLaB Amsterdam and Department of Physics and Astronomy VU University Amsterdam, 1081 HV Amsterdam, Netherlands.
authors.forename: Greg J
authors.initials: GJ
authors.lastname: Stephens
authors.affiliation: LaserLaB Amsterdam and Department of Physics and Astronomy VU University Amsterdam, 1081 HV Amsterdam, Netherlands.
authors.forename: Gijs J L
authors.initials: GJ
authors.lastname: Wuite
mesh_terms: D004247:DNA / Q000737:chemistry*; D004548:Elasticity; D008274:Magnesium / Q000737:chemistry*; D009690:Nucleic Acid Conformation; D009994:Osmolar Concentration
chemical_list: D004247:DNA; D008274:Magnesium