Conformation of B. stearothermophilus 5S ribosomal RNA.

The thermal melting of B. stearothermophilus 5S ribosomal RNA was studied, by means of derivative optical absorption and CD spectra, and high performance liquid chromatography, in Tris buffers with K+ and Mg2+ at pH 7.6. Biphasic changes in optical absorption and CD ellipticity were observed, which mean the melting of two helices. Change in molecular size was also examined in the melting process. The melting temperatures depended on ionic strength and concentration of Mg2+. Enhanced stability of the helix was indicated, as compared with the corresponding one in B. subtilis 5S ribosomal RNA. In the presence of a large amount of Mg2+, the third melting process was observed at low temperatures, which was suggested due to change in the tertiary structure.