title: Poly(rA).poly(rU) with Ni(2+) ions at different temperatures: infrared absorption and vibrational circular dichroism spectroscopy.
abstract: Phase transitions were studied of the sodium salt of poly(rA).poly(rU) induced by elevated temperature without Ni(2+) and with Ni(2+) in 0.07 M concentration in D(2)O (approximately 0.4 [Ni]/[P]). The temperature was varied from 20 degrees C to 90 degrees C. The double-stranded conformation of poly(rA).poly(rU) was observed at room temperature (20 degrees C-23 degrees C) with and without Ni(2+) ions. In the absence of Ni(2+) ions, partial double- to triple-strand transition of poly(rA).poly(rU) occurred at 58 degrees C, whereas only single- stranded molecules existed at 70 degrees C. While poly(rU) did not display significant helical structure, poly(rA) still maintained some helicity at this temperature. Ni(2+) ions significantly stabilized the triple-helical structure. The temperature range of the stable triple-helix was between 45 degrees C and 70 degrees C with maximum stability around 53 degrees C. Triple- to single-stranded transition of poly(rA).poly(rU) occurred around 72 degrees C with loss of base stacking in single-stranded molecules. Stacked or aggregated structures of poly(rA) formed around 86 degrees C. Hysteresis took place in the presence of Ni(2+) during the reverse transition from the triple-stranded to the double-stranded form upon cooling. Reverse Hoogsteen type of hydrogen-bonding of the third strand in the triplex was suggested to be the most probable model for the triple-helical structure. VCD spectroscopy demonstrated significant advantages over infrared absorption or the related electronic CD spectroscopy.
authors.affiliation: Department of Chemistry, Faculty of Science, University of Calgary, Calgary, Alberta T2N 1N4, Canada.
authors.forename: V
authors.initials: V
authors.lastname: Andrushchenko
authors.forename: Y
authors.initials: Y
authors.lastname: Blagoi
authors.forename: J H
authors.initials: JH
authors.lastname: van de Sande
authors.forename: H
authors.initials: H
authors.lastname: Wieser
mesh_terms: D055592:Biophysical Phenomena; D001703:Biophysics; D002942:Circular Dichroism; D007477:Ions; D008956:Models, Chemical; D009532:Nickel / Q000737:chemistry*; D009690:Nucleic Acid Conformation; D011061:Poly A / Q000737:chemistry*; D011063:Poly A-U / Q000737:chemistry*; D011072:Poly U / Q000737:chemistry*; D012492:Salts / Q000737:chemistry; D013055:Spectrophotometry, Infrared / Q000379:methods; D013696:Temperature
chemical_list: D007477:Ions; D012492:Salts; D011063:Poly A-U; D011061:Poly A; D011072:Poly U; D009532:Nickel