Single-chain Characteristics in Giant DNA 一 LargerHydrodynamic Radius in Circular than that in Linear

The conformation of polymer chains in dilute solution is the subject of first chapter in polymer physics. The sizes ofpolymer ， such as radius of gyration and hydrodynamic radius ， are important fundamental characteristics because they can be examined with experimental methods. For an ideal circular chain ， end-tかenddistance L=O by the definition ， and the gyration radius Rg is deduced as [1] <R;>αrcular = b2 N/12 =< R;>linear /2. where b isthe segment length and N is the number of segments. This indicates that the gyration radius in an ideal circular chain is smaller by a factor of J2 than that of linear chain of the same contour length. On the other hand ， the hydrodynamic radius RH in an ideallinear chain defined as the radius of hydrodynamically equivalent sphere is expected to be proportional and larger than the Rg as calculated仕omthe Zimm model. Thus ， itis expected that the hydrodynamic radius in circular chain is smaller than that in linear chain. As far as we know ， experimental verification of such theoretical expectation has not been established yet ， because it is difficult to synthesize monodisperse circular polymer. In this study ， we measured hydrodynamic radius of linear or circular DNA with 106 kilo base pairs using flωrescence microscopy (FM). To examin