Book of Abstracts: Albany 2005
The Influence of Ionic Strength on the Binding of Hoechst 33258 with DNA
Bis-benzimidazole Hoechst 33258 is known to bind with high specificity to the AT-sequences of DNA. Experiments carried out at ionic strengths 0.002 ≤ µ ≤ 0.02 M Na+ revealed at least two types of ligand binding with DNA. The first one has high affinity and specificity to AT sequences and the second one is the result of binding positively charged ligand with negatively charged phosphate groups of DNA. Experimental data showed that the melting temperature (Tm) and width of melting (ΔT) of complexes are increased in comparison with those of pure DNA at low ionic strength (µ = 0.002 M Na+ and at 0 ≤ rb ≤ 0.33, where rb is the ratio of ligand/polynucleotide phosphate) which allowed us to suggest that Hoechst 33258 binds with DNA by electrostatic mode at these conditions.
Increasing the ionic strength increases Tm and decreases ΔT of the complexes. The decrease of ΔT at ionic strength of solution µ ≥ 0.002 M Na+ suggests that electrostatic interaction reduces and ligand binds with high affinity and specificity to (A-T) rich sequences of B-DNA. The further increase in ligand concentration (rb ≥ 0.1) doesn?t result in change of ΔT due to the saturation of AT-rich sites of DNA by ligand.
This observation was supported by thermal denaturation experiments on ligand-different AT contents DNA complexes. The studies on melting showed that the value of the rb of saturation decreases with the decrease of AT content of the polynucleotides.
Poghos O. Vardevanyan1
1Department of Biophysics