Tying up molecules

A recent paper1xArai, Y. et al. Nature. 1999; 399: 446–448Crossref | PubMed | Scopus (184)See all References1 took manipulation of molecules with optical tweezers to a new level by showing that it is possible to tie knots in both actin filaments and DNA molecules (Fig. 1Fig. 1). Arai et al. attached polystyrene beads to the polymers, then used optical tweezers to manipulate these beads and hence the polymers themselves. In addition to tying knots, they recorded the tensile strength and flexibility of both the actin filaments and DNA molecules. As well as being an entertaining exercise, this approach has further practical applications. Tying a knot in a linear polymer generates a stable curvature that could be used as a basis for experimentation on, for example, the binding of associated proteins to curved versus straight polymer. Conceivably, knotting of such molecules could also be used to perturb cellular structure and observe the resulting effects.Fig. 1Tying a knot in a DNA molecule. A DNA molecule stained with POPO-3 was attached to two beads, and then movement of the beads using optical tweezers was used to generate various types of conformation, including knots, in the DNA molecule. Images 3–7 are accompanied by explanatory drawings depicting the conformation shown. The paper1xArai, Y. et al. Nature. 1999; 399: 446–448Crossref | PubMed | Scopus (184)See all References1 contains a similar set of images for actin, and other types of knot in DNA molecules. Bar, 10 μm.View Large Image | Download PowerPoint Slide