title: DNA psi-condensation and reentrant decondensation: effect of the PEG degree of polymerization.
abstract: Psi-condensation of DNA fragments of about 4 kbp was induced by poly(ethylene glycol) (PEG), with degrees of polymerization ranging from 45 to 182, and univalent salt (NaCl). Using circular dichroism spectroscopy, we were able to accurately determine the critical amount of PEG needed to induce condensation, as a function of the NaCl concentration. A significant dependence on the PEG degree of polymerization was found. Phase boundaries determined for the multimolecular condensation were very similar to those observed previously for the monomolecular collapse, with two asymptotic regimes at low and high salt concentrations. We analyze our data using a theoretical model that properly takes into account both the polyelectrolyte nature of the DNA and the liquid crystallinity of the condensed phase. The model assumes that all PEG is excluded from the condensates and shows reentrant decondensation only at low salt. We also systematically study reentrant decondensation and find a very strong dependence on PEG molecular weight. At low PEG molecular weight, decondensation occurs at relatively low concentrations of PEG, and over a wide range of salt concentrations. This suggests that in the reentrant decondensation the flexible polymers used are not completely excluded from the condensed phase.
authors.affiliation: Department of Physics, IBILCE UNESP, Universidade Estadual Paulista, R. Cristóvão Colombo 2265, 15054-000 São José do Rio Preto SP, Brazil.
authors.forename: José Esio Bessa
authors.initials: JE
authors.lastname: Ramos
authors.forename: Renko
authors.initials: R
authors.lastname: de Vries
authors.forename: João
authors.initials: J
authors.lastname: Ruggiero Neto
mesh_terms: D055598:Chemical Phenomena; D002627:Chemistry, Physical; D004247:DNA / Q000737:chemistry*; D011092:Polyethylene Glycols / Q000737:chemistry*; D011108:Polymers / Q000737:chemistry*
chemical_list: D011108:Polymers; D011092:Polyethylene Glycols; D004247:DNA