| Abstract: | Proflavine binding experiments were carried out with yeast rRNA, native and “unfolded” ribosomes; the binding constants and the number of binding sites were calculated by a spectroscopic method. The study of the intercalation complexes by fluorescence and electric dichroism shows the intercalation binding sites to involve two subtypes of sites, which could be related to different nucleotide composition and secondary structure of the rRNA regions, i.e., binding sites located in the (A + U)-rich single strands and binding sites located in the (G + C)-rich double-helical strands (fluorescence quenching sites). Electric dichroism of complexed proflavine is interpreted in terms of rRNA conformation within the ribosomes. The conclusions are in agreement with the ribosomal model of Cox and Bonanou and show that, according to this model, the base planes of the nucleotides are not all parallel in the native ribsome, but rather radiate around the folding axis of the ribonucleoprotein sheet. |
