Multi Factor Regulation Of DNA Aggreation

DNA condensation depends on many factors including valence and concentration of couterions,pH and dielectric properties of solution.In this study,we used atomic force microscopy（AFM）,dynamic light scattering（DLS）,and single-molecule magnetic tweezers（MT）to study the influencing factors and the synergistic effect on different factors of DNA condensation,decondensation,and charge neutralization,mainly include:1、The dielectric constant plays an important role in the charge neutralization after the interaction of ions and DNA.Study the regulation of the DNA charge neutralization induced by monovalent and divalent ions by changing of dielectric constant（adding 6-aminocaproic acid（6-A）and ethanol to adjust the dielectric constant of the solution）through DLS system.We found that the electrophoretic mobility of DNA decreases as the dielectric constant increases（addition of 0.25M6-A）in the presence of monovalent and divalent ions.On the contrary,we found the electrophoretic mobility of DNA gradually increases as the dielectric constant of the solution decreases（addition of different molar volumes fractional ethanol）.It can be seen that the increase of the dielectric constant has an inhibitory effect on the neutralization of DNA charge,and the decrease of the dielectric constant has a promoting effect on the neutralization of DNA charge.The greater the molar volume fraction of ethanol is,the stronger the promotion effect is.At the same time,under the same dielectric constant,the ratio of DNA mobility induced by Na⁺and Mg²⁺（5m M）is about 2:1,which is consistent with the Manning equilibrium theory.2、Dielectric constant and pH value can regulate DNA condensation.Study the effects of ielectric constant and pH on DNA condensation induced by Mg²⁺through AFM,DLS and MT（dielectric constant adjustment as above）.We found that With the decrease of pH and dielectric constant in Mg²⁺—DNA solution,DNA condensation was enhanced,and its condensation effect was stronger than that caused only by the decrease of pH or dielectric constant.It can be seen that pH and ethanol had synergistic effect on DNA condensation caused by Mg²⁺.Moreover,when zwitterion 6-A is added to DNA condenstes caused by ethanol and pH,deagglomeration occurs（the degree of condensation decreases）,It can be seen that both ethanol and 6-A have antagonistic effect on DNA condensation caused by Mg²⁺.The above results were further confirmed by MT,AFM and DLS.With the decrease of pH and dielectric constant in Mg²⁺—DNA solution,DNA condensation force and condensted degree became larger and stronger,with the increase of pH and dielectric constant,DNA condensation force and condensted degree became smaller and weaker.The mobility of DNA increased with the decrease of pH and dielectric constant of Mg²⁺—DNA solution,but it was always negative.