SUNY at Albany
June 19-23, 2001
Structural Transitions of Poly(rA)*Poly(rU) Induced by Ni(2+) Ions at Elevated Temperatures Studied by Vibrational Circular Dichroism (VCD) and IR Spectroscopy
The ability of poly(rA)*poly(rU) to exist in a triple helical form has been known for a while (1). However, some aspects of the double- to triple- and to single-stranded transitions as well as some structural details of the triple stranded form are still unclear. Triple-helical nucleic acids have been shown to play an important role in many biological processes, including specific protein binding and gene expression regulation via sequence-specific local triple helix formation (2).
The present study uses Vibrational Circular Dichroism spectroscopy, relatively new technique in the field. Partial double- to triple-strand transition of poly(rA)*poly(rU) was obtained in the absence of Ni(2+) ions. Significant stabilization of the triple-helical structure by Ni(2+) ions was shown. A stable triple-helical form was obtained in the presence of Ni(2+) ions in the wide temperature range from 45 to 70°C. Stacked or aggregated structures of poly(rA) formed around 86°C. Hysteresis can take place during the reverse transition from the triple-stranded to the double-stranded form upon cooling the sample in the presence of Ni(2+). 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. Several advantages were demonstrated by VCD spectroscopy compared to conventional IR absorption or the related Electronic CD spectroscopy.
References and Footnotes
V. Andrushchenko (1), J.H. van de Sande (2), Yu. Blagoi (3) and H.Wieser (1)
Department of Chemistry(1),