title: Studies on the negative circular dichroic bands around 297 nm of ribosomes from bacterial cells.
abstract: The small negative CD bands around 297 nm of isolated 30-S and 50-S ribosomal subunits were precisely measured for three bacteria, Bacillus stearothermophilus, Bacillus subtilis and Escherichia coli Q 13. The intensities of the negative CD bands of 30-S subunits were always much greater than those of 50-S subunits irrespective of the bacterial strains, which may be related to the difference in comformations of rRNAs and proteins in the complexes between these subribosomal particles. The dissociation of 70-S ribosomes into two subunits by lowering Mg2+ concentration caused evident enhancement of intensity of the 297 nm CD band, which was completely reversed by the association of the two subunits into 70-S particles. The melting profiles of CD spectra 3 B. stearothermophilus and E. coli were compared and both subunits of the former were found to be more heat stable than those of the latter. It was found that 5 M urea and 0.5% sodium dodecyl sulfate (SDS) treatment caused considerable reduction of the negative CD intensity around 297 nm of 30-S subunits but no significant change of 50-S subunits, while no significant change was observed for the CD spectra of isolated 16-S and 23-S rRNAs by the same treatment. Effects of EDTA treatment and then addition of Mg2+  on the CD spectra and fluorescence emission spectra of the subunits were also observed and the contribution by the interaction between rRNA s and proteins in ribosomes to the small negative band around 297 nm was discussed.
mesh_terms: D001412:Bacillus subtilis; D002942:Circular Dichroism; D004926:Escherichia coli; D001411:Geobacillus stearothermophilus; D006358:Hot Temperature; D008274:Magnesium / Q000494:pharmacology; D008970:Molecular Weight; D009690:Nucleic Acid Conformation; D012270:Ribosomes / Q000187:drug effects / Q000648:ultrastructure*; D012967:Sodium Dodecyl Sulfate / Q000494:pharmacology; D014508:Urea / Q000494:pharmacology
chemical_list: D012967:Sodium Dodecyl Sulfate; D014508:Urea; D008274:Magnesium