Experimental Study On The Effect Of Temperature And Ion Concentration On DNA Condensation

Recent fluorescent single molecule experiment indicated that the temperature can facilitate DNA condensation.In the spermine?spermidine?-DNA condensation system,DNA condensation conformation became more compact and orderly with temperature increasing.In order to detect the temperature effects in DNA condensation system further,we develop a temperature-changed ultraviolet Spectrum method.By applying the method to the condensation system mentioned by recent fluorescent single molecule experiment and the DNA in DI water,a conclusion was derived that the absorption value at 260 nm of a condensation system will be reduced,when the corresponding system is condensed further and become compact and orderly.Based on this conclusion,effects of temperature on DNA-Cobalt amine compounds used in DNA condensation experiments are detected by using temperature-changed ultraviolet Spectrum method.The results indicate that Hexaammine cobalt?III?chloride is similar to the spermine and spermidine,the UV absorption value at 260 nm of DNA reduces sharply with the temperature increasing,indicating that the DNA conformation tends to be more compact and orderly.However,for the condensation system wherein the DNA is condensed by tris?ethylenediamine?cobalt?III?chloride,trans-dichlorobis?ethylenediamine?cobalt?III?chloride and pentaamminechloro cobalt?III?chloride,respectively,the UV absorption value at 260 nm of the corresponding condensation System does not change with temperature monotonously,and takes an increased-reduced-increased manner.Then,by using Isothermal Titration Calorimetry?ITC?,we found that the binding constant between spermine and DNA gradually increased with the increasing temperature,indicating that spermine-DNA condensation system become more compact with increasing temperature.The binding constant between spermine and DNA can be reduced by NaCl,NaF,Na₂SO₄,Na₃PO₄,and their capacity to reduce the binding constant increase gradually,namely PO43->SO42->F->Cl-.Effect of Mg²⁺,Mn²⁺ on DNA condensation is different,with the increasing concentration of Mg²⁺,which makes the absorption value at 260 nm increased first and then decreased.However,the absorption value at 260 nm decreased gradually with the increasing concentration of Mn²⁺.At last,in order to investigate whether fluorine can form hydrogen bonds with DNA.A single molecule experiment was carried out by using ITC.It was found that NaF could bind to single-stranded DNA,and fluorine could form hydrogen bonds with the base of DNA.