Polyethylene Glycol(PEG) Induced DNA Condensation By Single Molecule Measurements

In this study, we investigated the DNA condensation induced by polyethylene glycol(PEG) with different molecular weights(PEG 600 and PEG 6000) in the presence of NaCl or MgCl2 by magnetic tweezers(MT), dynamic light scattering(DLS) and atomic force microscopy(AFM). The MT measurements show that with increasing NaCl concentration, the critical condensation force in PEG 600-DNA or PEG 6000-DNA system increased approximately linearly. PEG 6000 solution has a larger critical force than PEG 600 solution at a given NaCl concentration. In comparison, a parabolic trend of the critical condensation force was observed with increasing MgCl2 concentration, indicating that DNA undergoes a reentrant condensation. The AFM results show that the morphologies of the compacted DNA-PEG complexes depended on the salt concentration and were consistent with the MT results. We also try to ascertain the results by dynamic light scattering, but the conductivity of the solution is too high in the case of high concentration of salts, then the measurement is inaccurate.