Helical nature of poly(dI-dC).poly(dI-dC). Vibrational circular dichroism results.
Poly(dI-dC).poly(dI-dC) was studied using vibrational circular dichroism and IR spectroscopy in both the base deformation C = O and symmetric PO2- stretching regions. VCD spectra of this duplex under low salt conditions are consistent with its having a B-form structure. Addition of 5 M NaCl leads to relatively uniform VCD intensity loss which is consistent with loss of helical structure rather than formation of an intermediate state between the B and Z forms. This duplex polymer under high salt conditions with added NiCl2 shows aggregation effects, but its IR and VCD spectra have characteristic features of the Z-form DNA conformation. The cooperative change of backbone and base pair structure upon thermal denaturation is indicated by the simultaneous collapse of the VCD at 65 degrees C in both the PO2- and C = O stretching regions. This study further demonstrates that the VCD bandshape of a specific localized nucleic acid vibrational transition can be a useful indicator of the helical handedness. The empirical conformational interpretations are supported by simulated VCD spectra, which are in excellent agreement with the experimental results, based on dipole coupling calculations.
Department of Chemistry, University of Illinois at Chicago 60680.
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Wang
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Keiderling
D002942:Circular Dichroism; D009690:Nucleic Acid Conformation; D009691:Nucleic Acid Denaturation; D011089:Polydeoxyribonucleotides / Q000737:chemistry*; D013696:Temperature
D011089:Polydeoxyribonucleotides; C031156:poly d(I-C)