LASER MANIPULATION AND UV INDUCED SINGLE-MOLECULE REACTIONS OF INDIVIDUAL DNA-MOLECULES

Individual fluorescently labelled DNA molecules were bound to microbea ds. Controlled handling was. possible using a double beam optical trap and by electric fields but without the additional help of viscous dra g. Trapping and stretching of single molecules is shown under conditio ns where enzymes are active. After trapping the bead with optical twee zers and stretching the DNA in an electric field, an enzyme reaction w as started by UV photolysis of a caged compound for Mg2+ ions. The res triction endonuclease, ApaI cut the DNA molecule into two fragments. W hile one remained bound to the bead and fixed in the laser focus, the other fragment was dragged away towards the positive electrode. In con clusion, a single molecule--enzyme reaction recorded with a single pho ton counting camera and an image processing system is shown in a light microscope. (C) 1996 Elsevier Science B.V. All rights reserved.