UV resonance Raman study of PolyA and PolyU complexes: Mg2+-induced formation of PolyU•PolyA•PolyU triplexes

The 244-nm excited resonance Raman (RR) spectra of polynucleotides, namely polyA, polyU, and their mixtures forming polyA center dot polyU double helices and polyU center dot polyA center dot polyU triple helices, were measured with good spectral resolution, precise spectral calibration, and reliable intensity normalization. Difference spectra were constructed to visualize changes caused by the formation of the complexes and analyzed with respect to known interactions influencing the adenosine and uridine moieties in such complexes. This analysis enabled us to verify or to reject interpretations of certain Raman bands proposed in the literature. RR-monitored Mg2+ titration of an equimolar polyA and polyU mixture was performed to investigate the effect of induced triplex formation at a mM nucleoside concentration. The critical [Mg2+]/[phosphate] concentration ratio of approximately 12/1 was determined. (C) 2015 Elsevier B.V. All rights reserved.