Ionic strength effects on the stability and conformation of Penlctllium chrysogenum mycophage double stranded RNA

The effect of [Na+] on the stability and conformation of penicillium chrysogenum mycophage dsRNA (PCMdsRNA) was investigated using CD and UV optical techniques. Thermal melting profiles reveal prominent fine structure attributed to at least four regions of structural dissimilarity. A constant increased thermal stability of the dsRNA compared to DNA of the same base composition was observed over a concentration range of 1.5 times 10- minus 4 M to 4.5 times 10- minus 2 M Na+. At low ionic strengths ([Na+] less than 10- minus 3 M) Tm becomes independent of further decrease in [Na+] unless the dsRNA is exposed to high concentrations of EDTA, suggesting the involvement to tightly bound divalent cation. At relatively high ionic strengths ([Na+] greater than 0.1 M) a postulated A leads to A' ... conformation change occurs.