Fluorescence Methods for Probing G-Quadruplex Structure in Single- and Double-Stranded DNA.

Interest in exploring G-quadruplex (G4) structures in nucleic acids is growing as it becomes more widely recognized that these structures have many interesting biological roles and chemical properties. Probing the G4-forming potential of DNA with dimethyl sulfate, polymerase stop assays, or nuclease digestion are three commonly used techniques that usually employ radio-isotopic labels for visualization. However, as fluorescent labeling methods have grown in popularity and versatility, many laboratories have moved away from the routine use of radio-isotopic methods. We have adapted traditional procedures for structural analysis of G4-forming DNA sequences by using fluorescent labels and capillary electrophoresis and demonstrate their application to well-studied G4 structures, including c-MYC PU27 G4. The three fluorescent assays described here allow interrogation of G4 structures in double- and single-stranded DNA substrates, using either chemical or enzymatic cleavage. When combined, these techniques can provide valuable information for the investigation of G4 topology and structure, as well as visualizing any structural effects caused by interaction of quadruplexes with the complementary C-rich DNA strand.