Phase Transitions in the Higher Order Structure of Giant DNA

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As a whole, the international collaboration between Nagoya and Moscow has been performed successfully, including the development on basic concept in polymer physics and also in physical chemistry in mesoscopic system. Through the collaboration, the research group of Nagoya has demonstrated that individual single duplex DNA chains undergoes large discrete phase transition between elongated coil and compacted globule (coil-globule transition), based on the single chain observation by use of fluorescence microscopy, whereas ensemble of DNA has the characteristics of diffuse or continuous transition.From single chain observation, we found this first order phase transition is induced by various kinds of condensation agents such as synthetic polymer, cationic surfactant, low molecular multivalent cation, and alcohol. Based on these experimental findings, active collaboration between Nagoya and Moscow has been performed on the theoretical analysis of the phase transition in a single polymer chain, including Monte Carlo simulation and mean field theory. The essential aspects in the collapsed transition of long DNA chain has been reproduced with these theoretical analysis and calculations. It is to be noted that the existence of the morphological variation in the collapsed products can be interpreted well in these theories.