G-quadruplex structure and stability illuminated by 2-aminopurine phasor plots

Nucleic Acids Res. 2012 May;40(9):4203-15. doi: 10.1093/nar/gkr1286. Epub 2012 Jan 12.


The use of time-resolved fluorescence measurements in studies of telomeric G-quadruplex folding and stability has been hampered by the complexity of fluorescence lifetime distributions in solution. The application of phasor diagrams to the analysis of time-resolved fluorescence measurements, collected from either frequency-domain or time-domain instrumentation, allows for rapid characterization of complex lifetime distributions. Phasor diagrams are model-free graphical representations of transformed time-resolved fluorescence results. Simplification of complex fluorescent decays by phasor diagrams is demonstrated here using a 2-aminopurine substituted telomeric G-quadruplex sequence. The application of phasor diagrams to complex systems is discussed with comparisons to traditional non-linear regression model fitting. Phasor diagrams allow for the folding and stability of the telomeric G-quadruplex to be monitored in the presence of either sodium or potassium. Fluorescence lifetime measurements revealed multiple transitions upon folding of the telomeric G-quadruplex through the addition of potassium. Enzymatic digestion of the telomeric G-quadruplex structure, fluorescence quenching and Förster resonance energy transfer were also monitored through phasor diagrams. This work demonstrates the sensitivity of time-resolved methods for monitoring changes to the telomeric G-quadruplex and outlines the phasor diagram approach for analysis of complex time-resolved results that can be extended to other G-quadruplex and nucleic acid systems.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • 2-Aminopurine / chemistry*
  • DNA / chemistry
  • Fluorescence Resonance Energy Transfer
  • G-Quadruplexes*
  • Plant Proteins / metabolism
  • Single-Strand Specific DNA and RNA Endonucleases / metabolism
  • Telomere / chemistry*


  • Mung Bean Nuclease
  • Plant Proteins
  • 2-Aminopurine
  • DNA
  • Single-Strand Specific DNA and RNA Endonucleases