Studies on biomolecules using single molecule imaging and manipulation techniques

The best way to obtain unambiguous information about the function of biomolecules is to study their function at the single molecule level. By attaching a small tag such as a single fluorescent dye molecule to biomolecules, or a tag that is huge compared to the size of a biomolecule, we have been able to image the individual behaviours in real time under an optical microscope. Huge tags such as micrometer-sized plastic beads also allow the manipulation of individual molecules with, e.g. optical or magnetic tweezers. Using these techniques, we have observed individual behaviours, of RNA polymerase, a molecular machine that copies the genetic information on DNA onto a messenger RNA. We found that some of the RNA polymerase molecules underwent linear diffusion along DNA, helping RNA polymerase to search for the promoter. We also found that a single RNA polymerase molecule rotated around the right-handed screw axis of the double helix of DNA during transcription with a rotary torque of > 5 pN nm. The present methods are potentially applicable to the examination of a wide variety of protein-nucleic acid interactions, especially those involved in the process of transcription. (C) 2004 Elsevier Ltd. All rights reserved.