Single Molecule Research Of DNA Condensation And Charge Inversion

The detection and manipulate of DNA, the core material of life, is currently one of the hot spot of biological research in a single molecular level, and DNA condensation and charge reversal is the core of molecular biology. In this paper, we study DNA condensation and DNA charge inversion by single molecule technology. The main contents are as fellows:1. We performed systematic studies of DNA condensation induced by [Co(NH3)6]3+using molecular combing method and dynamic light scattering. It is found that the average extension of λ-DNA-YOYO-1complex is20.9μm, which is about30%longer than the contour length of the DNA in TE buffer, due to bis-intercalation of YOYO-1. A multivalent cation, Hexammine cobalt, is used for DNA condensation. The result indicated that the length of DNA-[Co(NH3)6]3+complexes decreased from20.9μm to5.9μm, as the concentration of the [Co(NH3)6]3+varied from0to3μM. This observation provides a direct visualization of single DNA condensation induced by hexammine cobalt. The results from the molecular combing studies are supported by dynamic light scattering (DLS) investigation, where the average hydrodynamic radius of the DNA complex decreases from203.8nm to39.26nm under the same conditions. Furthermore, we found that the zeta potential of DNA is invariant by measuring the zeta potential of DNA in the presence and absence of YOYO-1. It confirmed that the presence of YOYO-1didn’t affect the interaction between DNA and[Co(NH3)6]3+. Finally, we provided the mechanism of stretching DNA under different conditions.2. As some widely used condensed agent for DNA condensation, spermine and protamine are used to induce single molecule DNA condensation. The condensed degree of DNA increases with increasing the concentration of condensed agent as spermine. However, when the concentration of spermine is above the critical value, the DNA charge inversion can be observed. Here, we demonstrate the time-dependent mobility of λ DNA with adding different concentration of multivalent ions by self-restraint Electrophoresis Slot (ES). All samples were observed after incubating about30min at room temperature. For concentration c=1mM of the quadrivalent cation spermine ([C10N4H30]4+), the mobility became less negative with increasing drift time of DNA condensates. When the drift time of DNA is greater than the charge-inversion time t0=220s, the mobility became positive. With the drift time became greater, the mobility of DNA tend to be a constant finally. It showed that the binding of spermine became saturation. Further increasing the spermine concentration to5mM, charge inversion occurred immediately after incubation. This is to our knowledge the first experimental report of DNA charge inversion versus time induced solely by simple multivalent ions. Furthermore, it found that the stretched length of DNA elongated with the increase of DNA mobility. Meanwhile, we repeated our measurements using salmon protamine at physiological salt concentrations. Under different concentration of protamine, the similar phenomenon of charge inversion can be observed. By observing the charge inversion versus time induced by multivalent ions, we further provided the mechanism of DNA charge inversion.