Efficient procedure of preparation and properties of long uniform G4-DNA nanowires.

Here we describe a novel and efficient procedure for preparation of long uniform G4-DNA wires. The procedure includes (i) enzymatic synthesis of double-stranded DNA molecules consisting of long (up to 10,000 bases), continuous G strands and chains of complementary (dC)20-oligonucleotides, poly(dG)-n(dC)20; (ii) size exclusion HPLC separation of the G strands from the (dC)20 oligonucleotides in 0.1M NaOH; and (iii) folding of the purified G strands into G4-DNA structures by lowering the pH to 7.0. We show by atomic force microscopy (AFM) that the preparation procedure yielded G4-DNA wires with a uniform morphology and a narrow length distribution. The correlation between the total amount of nucleotides in the G strands and the contour length of the G4-DNA molecules estimated by AFM suggests monomolecular folding of the G strands into quadruplex structures. The folding takes place either in the presence or in the absence of stabilizing ions (K+ or Na+). The addition of these cations leads to a dramatic change in the circular dichroism spectrum of the G4-DNA.

Preparation and duplex-to-single strand transition of the fully complementary duplex of d(G4).d(C4) in aqueous solution.

The d(G4) and d(C4) molecules in the single stranded state were synthesized by the phosphotriester method and purified. The full duplex of tetramer d(G4).d(C4) was prepared by expending about a month. The duplex-to-single strand transition was observed by UV-spectroscopy. A standard hypochromic effect was observed, which is different from some experimental results reported previously.