Movies of single-molecule trapping experiments

Tether assembly

To perform single molecule force spectroscopy we need to assemble a tether between two beads. One of the beads is held at the end of a micropipette tip and the other one in an optical tweezer. For the insitu tether assembly we use a three channel design micro flow-chamber. The trapping experiment takes place in the central channel, and the bottom and top channels are used for bead exchange. The movie shows the assembly process. First the flow-chamber is moved, so that the position of the optical trap is in the vicinity of a so called bead dispenser, which is a connection to the lower flow channel. A bead is trapped in the optical trap, and the chamber repositioned to bring the trap to close vicinity of the end of the micropipette. Then the bead is transferred to the pipette by suction. In a next step, the next bead is grabbed from the second dispenser. The last step is the actual formation of the tether. The beads are brought into close contact and the succesful tether formation is visualized by a small black bar at the right side of the screen that indicates the measured force. Download the assembly movie (5.1 MB)

Constant force viral DNA packaging

The movie shows a single run of DNA packaging by the viral portal domain motor-complex of bacteriophage phi29. During the experiment the force is measured continously and held constant by a feedback loop that changes the position of the micropipette, while leaving the position of the optical trap unchanged. As the motor is packaging and the length of the DNA tether is decreasing, the pipette is moved upwards. Download the phage packaging movie (3.4 MB)

All experiments described on this page were done in the lab of Carlos Bustamante at UC Berkeley, together with Yann Chemla and Aathavan, in collaboration with the lab of Dwight Anderson at the University of Minnesota. Previous experiments on the phi29 packaging motor in the Bustamante lab were carried out by Doug Smith and Sander Tans, their experiments were published in Nature ( Download paper ). More recently investigated the mechanism of force generation of the packaging motor. The results are published in Cell ( Download paper ).

Thanks to Yann Chemla for making the movies.

Eukaryotic transcription
The movie is an animation of yeast RNA polymerase II (Pol II) single-molecule transcription data obtained in passive mode. The work is described in our recent publication in Physics of Life Reviews (Download paper ). Download the Pol II transcription movie (compressed using xvid)