A two-state conformational equilibrium for alternating (A-T)n sequences in negatively supercoiled DNA. Academic Article uri icon

Overview

MeSH

  • Base Sequence
  • Osmium Tetroxide
  • Plasmids
  • Repetitive Sequences, Nucleic Acid
  • Temperature
  • Thermodynamics

MeSH Major

  • Adenine
  • DNA, Superhelical
  • Nucleic Acid Conformation
  • Thymine

abstract

  • We have made a study of the pattern of osmium tetroxide modification in supercoiled plasmids containing alternating (A-T)n tracts. Two distinct alternative patterns may be obtained, depending upon conditions. At moderate salt concentrations, or at low temperature, only thymine bases close to the centres of the tracts were modified, consistent with the presence of a cruciform structure. At higher temperatures in the absence of cations, uniform modification throughout the tracts was observed. The cationic concentration required to stabilize cruciform structure depends markedly on its charge, and a number of transition metal ions were totally ineffective. The results are interpreted in terms of a two-state equilibrium between the cruciform and a perturbed helical structure, the position of which is temperature- and salt-dependent. For longer (A-T)n tracts, a third pattern of osmium tetroxide modification is found at intermediate salt concentrations, consistent with a cruciform having an extensively disrupted four-way junction.

publication date

  • October 20, 1987

has subject area

  • Adenine
  • Base Sequence
  • DNA, Superhelical
  • Nucleic Acid Conformation
  • Osmium Tetroxide
  • Plasmids
  • Repetitive Sequences, Nucleic Acid
  • Temperature
  • Thermodynamics
  • Thymine

Research

keywords

  • Journal Article

Identity

Language

  • eng

PubMed ID

  • 3430599

Additional Document Info

start page

  • 707

end page

  • 721

volume

  • 197

number

  • 4