EVIDENCE FOR GLOBAL MOBILITY IN THE PREMELTING OF A POLYNUCLEOTIDE FROM TEMPERATURE-DEPENDENT RAMAN OPTICAL-ACTIVITY

The backscattered Raman and Raman optical activity (ROA) spectra of po ly(rA) -poly(rU) at 20 degrees C and 45 degrees C in buffered aqueous solution between 650 and 1750 cm(-1) are reported. Although the intens ity of the majority of the Raman bands increase by varying amounts as the temperature is raised in accordance with the well-known hypochromi c effect, the reverse effect is found for the ROA signals which we att ribute to thermal accessibility of a greater number of distinct confor mations leading to cancellation of ROA signals. The difference ROB spe ctrum obtained by subtracting the spectrum recorded at 45 degrees C fr om that recorded at 20 degrees C displays a very similar sign pattern to those at both 20 degrees C and 45 degrees C throughout the spectral region examined. This indicates that the same average structure is ma intained in this temperature range and that the thermal fluctuations a re correlated through the bases, the glycosidic link, the sugar ring, and the phosphate backbone of both strands. These results indicate tha t ROA may be a useful new probe of the dynamics of nucleic acid in sol ution. (C) 1998 John Wiley & Sons, Inc.