STUDY OF TOLUIDINE BLUE-RIBOSOMAL RNA COMPLEXES

1. Toluidine blue forms two types of complexes with rRNA depending on the molar ratios of dye and rRNA nucleotides. (a) Complex I, formed in the presence of excess of rRNA shows a negative metachromasia and unmodified electrophoretic mobility as compared to uncomplexed rRNA. Saturation of this type of complex appears to occur when one molecule of dye corresponds to six rRNA nucleotides. (b) Complex II, characterized by a positive metachromasia and a modified electrophoretic mobility, predominates when the molar ratio of toluidine blue to rRNA nucleotide is almost 1:1. At intermediate ratios of dye and nucleotides, both complexes are present at the same time. 2. Physicochemical properties of Complex I suggest that in this case toluidine blue is intercalated between the adjacent pairs of bases, whereas those of Complex II indicate that the dye is attached to the negative charged phosphate groups of rRNA nucleotides. 3. The presence of toluidine blue in the rRNA solution has a stabilizing effect on the secondary structure of rRNA. The transition of the stacked regions to unstacked regions in the rRNA, which is complexed with toluidine blue (Complex I and II), occurs at higher temperatures than with the uncomplexed rRNA. At the same time toluidine blue contributes to reformation of the stacked regions of rRNA upon cooling. © 1969.