Physical properties of the E. coli 4.5s RNA: First results suggest a hairpin helix of unusual thermal stability

Abstract

Hyperchromicity measurements and quasi-elastic laser light scattering (QELS) have been used to assess the solution structure of the metabolically stable E. coli 4.5S RNA Results from thermal denaturation measurements revealed the 4.55 species to be markedly more stable than most other RNAs characterized thus far. Optical Tm's range from 79° to 88° with transitions ̃25°C wide The Tm values show little dependence on ionic strength, but stability is enhanced considerably by Mg+2 . In the QELS experiments the diffusion coefficient does not decrease until T > 70°C. Neither the diffusive melting nor the diffusion coefficient at infinite dilution (D20,w°) show dependencies on ionic strength but both are influenced by Mg+2 . The diffusion behavior is in agreement with that predicted for a rigid cylindrical molecule 125 to 160 A long and 37 to 26 Å in diameter. Taken together these results are consistent with the more stable hypothetical secondary structures that can be formed, in which 70-75% of the 114 bases are paired to form a single extended hairpin helix. © 1984 IRL Press Limited.