Discrimination of G-Quadruplexes from Duplex and Single-Stranded DNAs with Fluorescence and Energy-Transfer Fluorescence Spectra of Crystal Violet

G-rich nucleic acid sequences with the potential to form G-quadruplex structures are common in biologically important regions. Most of these sequences are present with their complementary strands. so the development of a sensitive biosensor to distinguish G-quadruplex and duplex structure and to determine the competitive ability of quadruplex to duplex structures has received a great deal of attention. In this work. the interactions between two triphenylmethane dyes (malachite green (MG) and crystal violet (CV)) and G-quadruplex, duplex. or single-stranded DNAs were studied by fluorescence spectroscopy and energy-transfer fluorescence spectroscopy. Good discrimination between quadruplexes and duplex or single-stranded DNAs can be achieved by using the fluorescence spectrum of CV or the energy-transfer fluorescence spectra of CV and MG. In addition, by using energy-transfer fluorescence titrations of CV with G-quadruplexes, the binding-stoichiometry ratios of CV to G-quadruplexes call be determined. By using the fluorescence titrations of G-quadruplex-CV complexes with C-rich complementary strands, the fraction of G-rich oligonucleotide that engages in G-quadruplex structures in the presence of the complementary sequence can be measured. This Study may provide a simple method for discrimination between quadruplexes and duplex or single-stranded DNAs and for measuring G-quadruplex Percentages in the presence of the complementary C-rich sequences.