Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

A New Twist on DNA

17.07.2003


Using a tool kit of lasers, tiny beads and a Lego set, Howard Hughes Medical Institute researchers have made the first measurement of the torsional, or twisting, elasticity of a single molecule of DNA.



The measurements reveal that DNA is significantly stiffer than previously thought and, when wound, may in fact provide enough power to be used as a sort of molecular, rubberband motor to propel nanomachines. Although that type of application may be well in the future, the studies are significant because they offer a blueprint for measuring the contortions that DNA undergoes during replication and other key processes.

The researchers, led by Howard Hughes Medical Institute investigator Carlos Bustamante, reported their research in the July 17, 2003, issue of the journal Nature. Bustamante and the paper’s two lead authors, graduate students Zev Bryant and Michael Stone, are at the University of California, Berkeley.


“This finding is important because many of the processes involved in reading the information in DNA involve distorting the DNA molecule,” said Bustamante. “And to truly understand these processes, we need to understand the energy costs involved in the interaction between the protein that induces distortion and the DNA.”

Almost ten years ago, Bustamante and his colleagues measured the extensional elasticity of single-strand DNA, by attaching a DNA molecule at either end to tiny beads. Using a laser “magnetic tweezers” instrument, the researchers applied a precisely known force to stretch the molecule. However, measuring the torsional stiffness of the molecule proved far more difficult.

“For almost seven years, I couldn’t convince any graduate student or postdoc to do these experiments,” said Bustamante. “I would tell them my idea, which I thought was really great, and they would look at me, smile and say, `Yeah, yeah, great, nice idea … next?’ Finally, Zev and Mike came to my office and said, `We’re going to try this crazy experiment of yours. It’s not going to work, but we’ll try it, anyway.’”

Bustamante’s scheme involved attaching the ends of a single DNA molecule between two tiny beads as they had done before. However, in the torque-measurement experiments, the researchers then biochemically “nicked” a point on the double-strand DNA to create a single chemical bond swivel. Near this nick, on the side of the rotating bead, the researchers attached a third “indicator” bead. They then rapidly wound the DNA molecule up thousands of times — while holding the rotor bead steady with flow — using a twisting robot built from Legos. After the winding process, they stopped the flow and followed the unwinding of the DNA molecule by looking at the spinning of the rotor bead in real time.

By measuring the resulting spins of a series of indicator beads of differing diameters as the molecule untwisted, the researchers obtained data that they could analyze to measure the DNA molecule’s torsional stiffness.

Bustamante and his colleagues discovered from this analysis that the DNA molecule was about 40 percent more resistant to twisting than had been reported by other researchers. “We’re very surprised and excited about this finding because it represents the first direct measurement of the torsional stiffness of a single DNA molecule,” said Bustamante. “The other measurements were done on molecules in bulk, and were indirect.”

According to Bustamante, the conclusive measurement of torsional elasticity will enable researchers to understand better the “partitioning” of mechanical energy as a DNA molecule undergoes twisting during biological processes. While some fraction of the energy twists the double-stranded spiral of the molecule itself, another fraction creates “writhing” — a hairpin looping of the molecule like an over-twisted rope. “This value of forty percent more tells us we may need to revise our ideas about such partitioning,” said Bustamante.

Importantly, he said, the ability to measure molecular torque will enable a new class of experiments to study the mechanical behavior of protein enzymes that interact with the DNA molecule. For example, Bustamante and his colleagues are now using the same experimental apparatus to explore how the enzyme DNA polymerase — which copies a single DNA strand by pulling itself along the strand’s length — exerts torque on the DNA strand as it works.

More speculative, said Bustamante, is the idea that the DNA molecule might provide energy to power molecule-sized nanomotors. “We found that if you pull the DNA molecule, it will overstretch and must unwind. During this process, the mechanical linear force applied to the end of the molecule gets transformed into the generation of torque. If you relax the molecule, it will rewind, generating torque in the opposite direction. The molecule then behaves as a reversible force-torque converter,” said Bustamante. “If you attached rotational elements to the molecule, when you pulled the molecule, it would begin rotating and would drive the molecule as a motor.”

Contact: Jim Keeley, keeleyj@hhmi.org

Jim Keeley | Howard Hughes Medical Institute
Further information:
http://www.hhmi.org

More articles from Life Sciences:

nachricht Cnidarians remotely control bacteria
21.09.2017 | Christian-Albrechts-Universität zu Kiel

nachricht Immune cells may heal bleeding brain after strokes
21.09.2017 | NIH/National Institute of Neurological Disorders and Stroke

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Highly precise wiring in the Cerebral Cortex

Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.

The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...

Im Focus: Tiny lasers from a gallery of whispers

New technique promises tunable laser devices

Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...

Im Focus: Ultrafast snapshots of relaxing electrons in solids

Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!

When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...

Im Focus: Quantum Sensors Decipher Magnetic Ordering in a New Semiconducting Material

For the first time, physicists have successfully imaged spiral magnetic ordering in a multiferroic material. These materials are considered highly promising candidates for future data storage media. The researchers were able to prove their findings using unique quantum sensors that were developed at Basel University and that can analyze electromagnetic fields on the nanometer scale. The results – obtained by scientists from the University of Basel’s Department of Physics, the Swiss Nanoscience Institute, the University of Montpellier and several laboratories from University Paris-Saclay – were recently published in the journal Nature.

Multiferroics are materials that simultaneously react to electric and magnetic fields. These two properties are rarely found together, and their combined...

Im Focus: Fast, convenient & standardized: New lab innovation for automated tissue engineering & drug

MBM ScienceBridge GmbH successfully negotiated a license agreement between University Medical Center Göttingen (UMG) and the biotech company Tissue Systems Holding GmbH about commercial use of a multi-well tissue plate for automated and reliable tissue engineering & drug testing.

MBM ScienceBridge GmbH successfully negotiated a license agreement between University Medical Center Göttingen (UMG) and the biotech company Tissue Systems...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

“Lasers in Composites Symposium” in Aachen – from Science to Application

19.09.2017 | Event News

I-ESA 2018 – Call for Papers

12.09.2017 | Event News

EMBO at Basel Life, a new conference on current and emerging life science research

06.09.2017 | Event News

 
Latest News

Comet or asteroid? Hubble discovers that a unique object is a binary

21.09.2017 | Physics and Astronomy

Cnidarians remotely control bacteria

21.09.2017 | Life Sciences

Monitoring the heart's mitochondria to predict cardiac arrest?

21.09.2017 | Health and Medicine

VideoLinks
B2B-VideoLinks
More VideoLinks >>>