Abstract
AbstractThe unfolding of B. subtilis 5S RNA is examined by direct calorimetric measurement in the presence of various concentrations of Na+ and Mg2+. The composite differential scanning calorimetry (DSC) curve is analyzed into 3–5 individual two‐state melting transitions. In the absence of added Na+ or Mg2+, the 5S RNA segments melt together at Tm = 40°C. Addition of Na+ stabilizes the molecular structure (Tm = 56°C) and widens the melting temperature range, so that up to five component transitions are observed. Addition of Mg2+ alone produces a very stable structure (Tm = 75°C) with highly cooperative melting. Finally, addition of both Na+ and Mg2+ produces the highest stability (Tm = 76°C). The results are interpreted according to hypothetical secondary and tertiary base‐pairing schemes. The conformational changes demonstrated here may facilitate the movement of the protein synthesis machinery during RNA translation.
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