SECONDARY STRUCTURE EFFECTS ON THE INTERACTION OF DIFFERENT POLYNUCLEOTIDES WITH CA-2+

The interaction of Ca2+ ions in 10 mM NaCl at 17°C with polynucleotides of different primary and secondary structure has been investigated. The experimental results show the following: The affinity for calcium ion depends on the secondary structure of the polynucleotide and not, within the experimental error, on the base sequence. The following hierarchy in calcium ion binding can be established: A‐RNAs > B‐DNAs > single‐stranded RNAs. The polyG binding curve is analogous to that of A‐RNAs; this strongly suggests that it does not adopt a single‐stranded structure in our experimental conditions. Apart from the case of single‐stranded RNAs, where both Manning's and Poisson–Boltzmann models seem to fit the data well, the Poisson–Boltzmann equation reproduces the experimental points better than the Manning's theory, which overestimates the affinity of the double‐stranded nucleic acids for calcium ion. Copyright © 1990 John Wiley & Sons, Inc.