title: Overcoming potassium-mediated triplex inhibition.
abstract: Sequence-specific duplex DNA recognition by oligonucleotide-directed triple helix formation is a possible approach to in vivo gene inhibition. However, triple helix formation involving guanine-rich oligonucleotides is inhibited by physiological ions, particularly K+, most likely due to oligonucleotide aggregation via guanine quartets. Three oligodeoxynucleotide (ODN) derivatives were tested for their ability to resist guanine quartet-mediated aggregation, yet form stable triplexes. Electrophoretic mobility shift and dimethyl sulfate footprinting assays were used to analyze the formation of triplexes involving these oligonucleotide derivatives. In the absence of K+, all ODNs had similar binding affinities for the duplex target. Triplexes involving a 14mer ODN derivative containing 7-deazaxanthine substituted for three thymine bases or an 18mer ODN containing two additional thymines on both the 5' and 3' termini were abolished by 50 mM K+. Remarkably, triplexes involving an ODN derivative containing four 6-thioguanine bases substituted for guanine resisted K+ inhibition up to 200 mM. We hypothesize that the increased radius and decreased electronegativity of sulfur in the 6-position of guanine destabilize potential guanine quartets. These results improve the prospects for creating ODNS that might serve as specific and efficient gene repressors in vivo.
authors.affiliation: Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha 68198-6805, USA.
authors.forename: W M
authors.initials: WM
authors.lastname: Olivas
authors.forename: L J
authors.initials: LJ
authors.lastname: Maher
mesh_terms: D000818:Animals; D001483:Base Sequence; D008958:Models, Molecular; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D009841:Oligonucleotides / Q000737:chemistry* / Q000378:metabolism; D011188:Potassium / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D009841:Oligonucleotides; D011188:Potassium