[Circular dichroism spectra study on the ribonucleoprotein structure of influenza virus]

The CD spectra of Influenza virus RNA and RNP were examined in the ultraviolet region (220--320 nm) at different temperatures, NaCl and urea concentrations. The magnitude of the positive band for RNP decreases gradually upon increasing the temperature, indicating that rather weak interaction between RNA and protein occurs. However the temperature drastically affects the intensity of the negative band about 222 nm. In the temperature range where the protein melts the positive band at longer wavelengths shows a temperature dependence that is similar for RNP and free RNA. Addition of NaCl results in an increase in intensity and blue shift of the positive CD band of RNP. In the presence of 1 M NaCl the CD spectrum of RNP is very close to that of protein-free RNA. Urea concentrations up to 10 M has little effect on the CD spectrum of RNP. These results suggest that only ionic but not hydrophobic and hydrogen bondings are involved in the RNA-protein interaction in Influenza virus RNP.