Kinetics of collapse and decollapse of a single double-stranded DNA chain

Transition of a single duplex DNA between elongated coil and condensed globule has been studied by the technique of single molecular observation with fluorescence microscopy. It has become clear that individual DNA chains undergo first-order phase transition. We have observed the time-dependent change of the DNA structure accompanied with the phase transition from coil to globule. The speed of the compaction was found to be almost constant along the DNA chain. It is indicated that the coil-globule transition exhibits the phenomenon of “nucleation and growth”. The process of the decollapse of a single DNA has also been observed, the time dependence of the long axis length being described as l ∼ t^1.8.