Assembled Structure And Characterization Of G-rich DNA

Following the study of DNA molecules as the material of nano-medicament andnano-machine, or as the template coding for functional protein micro-equipments, wegradually realize that except for the conventional function of nucleic acids as thecodes of life, there are more potential for them to be used in nanotechnology, becauseof their denatured-renatured character and molecular recognition properties.The structures of nucleic acid show the tendency of polymorphism. Besides theusual anti-parallel structures of DNA double helix, DNA sequences can also constructunusual topological structures such as Triplexes, Quadruplexes or Holliday Junctions.Recently several G-rich sequences have been found existing at critical chromosomalsites in eukaryotic genome, and suggested to be related to important biologicalfunctions in vivo. Meanwhile, the G-wires species formed from consecutivequadruplexes appear certain structural and functional properties of nano-machines,which extend the functions of DNA to non-biological areas. So interests in this studyis none other than the G-quadruplexes formed from G-rich sequences, which give theDNA molecules more chances to be used in future gene-therapy researches andnanotechnology developments. By using Ultraviolet (UV) and Circular Dichroism (CD) spectroscopy we study theeffect of cationic species, pH values in solution and discrepancy of sequences on thestructures of G-rich DNAs and their complements. In addition, we improve themethods of identifying Frayed Wires DNA conformations, which formed fromdistinctive G-rich oligonucleotides and have much potential to be utilized innano-machine developments. And we observe the appearance of structures formedfrom G-rich oligonucleotides in solution by TEM. The results indicate that it isnecessary in the cationic conditions that the G-rich oligonucleotides can form seniorstructures G-quadruplexes, but they show high selectivity to counter-ion species.While the pH values of solution mainly affect their complementary C-rich sequences,which under certain conditions can form special structure called I-motif. On the otherhand, Frayed Wires DNA does not show strong discrimination to cation kinds, but thecationic condition is more helpful to structural stabilization. Although Frayed WiresDNAs show extraordinary high thermodynamic stability, they are readily to bedestroyed by relative complementary C-rich sequences. What is more, TEM picturesconfirm that the structure of G-rich sequences concluded by spectra methods.