DNA condensation induced by a cationic polymer studied by atomic force microscopy and electrophoresis assay

We synthesized a cationic polymer, poly(PEGMA)-4N, which has brush-like chains and four positively charged amino groups at the end of the molecules. DNA condensation induced by poly(PEGMA)-4N was investigated through electrophoresis assay by its ability to retard DNA mobility and to inhibit HindIII enzyme cleavage. The detailed structures of DNA condensates induced by poly(PEGMA)-4N were observed through atomic force microscopy (AFM). Interactions between polymers and DNA are mainly attributed into depletion effect and electrostatic interaction. Positively charged amino groups in poly(PEGMA)-4N interact with DNA through electrostatic interaction, and depletion effect also takes effect because poly(PEGMA)-4N is a flexible polymer. Comparing the contributions that the two interactions gave in DNA condensation process, we found that depletion effect played a major role compared with electrostatic interaction.