Tying a Knot in an Actin Filament




Polystyrene beads were attached to the ends of an actin filament.  The two beads were each held in an optical trap, and one bead was manipulated to knot the filament.  To let the moving end cross the filament on the desired side, the microscope focus was shifted slightly up or down.  Note that the transparent grip by the optical tweezers allows knotting without a shift of the grip.  The actin filament broke at the knot when the radius of curvature became too small.
                                                               Arai, Y. et al., Nature 399, 466-468 (1999).