Morphological Variation of Higher Order Structure of Long Duplex DNA and its genetic activity

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Compaction of DNA is a common feature in native genomes, e.g., in chromatin or phage heads. The manner of packaging is expected to play an essential role in the biological functions of DNA, such as replication and transcription.I have made direct observations on the conformational change of individual long duplex DNA molecules using fluorescence microscopy. It has been shown that giant DNAs exhibits an all-or-none change, or switching, in the folding transition. I have also reported that complexes of DNA-histone HI form a pearl necklace-like structure when the complexes were prepared by a natural dilution from a high salt solution to a low salt solution. In addition, we have applied laser-tweezers to manipulate the DNA-histone H1 under the real time observation with fluorescence microscopy. When the DNA-H1 complex is optically transported from a low-salt solution to a high-salt solution, its conformation changes from a compact to an elongated structure. With the reverse procedure, the elongated chain shrinks into a compact state. Laser manipulation is expected to be a powerful tool for research on the dynamics of various biomolecules mimicking intracellular processes.