Abstract
Compaction of DNA is a common feature in native genomes. The manner of packaging is expected to play an essential role in the biological functions of DNA, such as replication and transcription. We have studied the conformational change of long duplex DNA molecules through single molecular chain observation using fluorescence microscopy. It has been found that individual DNA molecules undergo large discrete transition between elongated coil and folded compact states. We have examined the effect of various chemical species on the higher order structure of giant DNA molecules. It has been shown that DNA molecules take rich variety of different morphologies, including intra-chain segregation, pearling structure, and spool like structure and that a strong correlation was found between the morphology of DNA and the sensitivity to restriction enzyme activities. It has also been found that on/off change in the transcriptional activity is induced accompanied by the transition of higher order structure on DNA. It is expected that the application of single chain observation will be useful to shed light on the mechanism of radiation damage on DNA molecules. [J Radiat Res 44:381 (2003)]
