Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Relaxation helps pack DNA into a virus

27.05.2014

Researchers at the University of California, San Diego have found that DNA packs more easily into the tight confines of a virus when given a chance to relax, they report in a pair of papers to be published in in the early edition of the Proceedings of the National Academy of Sciences the week of May 26 and the May 30 issue of Physical Review Letters.

DNA is a long, unwieldy molecule that tends to repel itself because it is negatively charged, yet it can spool tightly. Within the heads of viruses, DNA can be packed to near crystalline densities, crammed in by a molecular motor.


This image shows cross-sections of the empty prohead of the bacteriophage phi29 (left) and the fully assembled virus (right). A molecular motor transports the DNA (red) into the prohead through a portal. Higher resolution TIFF image available.

Credit: Jingua Tang and Timothy Baker, University of California, San Diego

"These are among the most powerful molecular motors we know of," says Douglas Smith, a professor of physics whose group studies them.

Within an infected cell, viruses assemble in a matter of minutes. Smith's group studies the process by isolating components of this system to watch single molecules in action.

... more about:
»DNA »Relaxation »equilibrium »knots »matter »viruses

They attach the empty head of a single virus, along with the molecular motor, to a microscopic bead that can be moved about using a laser. To another bead, they tether a molecule of viral DNA.

"It's like fishing," Smith says. "We dangle a DNA molecule in front of the viral motor. If we're lucky, the motor grabs the DNA and starts pulling it in."

Packaging proceeds in fits and starts, with slips and pauses along the way. These pauses increase, along with forces the motor counters, as the viral head becomes full.

Scientists who model this process have had to make assumptions about the state of the DNA within. An open question is whether the DNA is in its lowest energy state, that is at equilibrium, or in a disordered configuration.

"In confinement, it could be forming all kinds of knots and tangles," said Zachary Berndsen, a graduate student in biochemistry who works with Smith and is the lead author of the PNAS paper.

To figure this out, Berndsen stalled the motor by depriving it of chemical energy, and found that packaging rates picked up when the motor restarted. The longer the stall, the greater the acceleration.

DNA takes more than 10 minutes to fully relax inside the confines of a viral head where there's little wiggle room, the team found. That's 60,000 times as long as it takes unconfined DNA to relax.

"How fast this virus packages DNA is determined by physics more than chemistry," Smith said.

DNA's tendency to repel itself due to its negative charge may actually facilitate the relaxation. In related experiments, the researchers added spermidine, a positively charged molecule that causes DNA in solution to spool up.

"You might think the stickiness would enhance packing, but we find that the opposite is true," said Nicholas Keller, the lead author of this second report, published in Physical Review Letters.

Countering the negative charges, particularly to the point of making the DNA attractive to itself, actually hindered the packaging of DNA.

"The DNA can get trapped into conformations that just stop the motor," Keller said.

"We tend to think of DNA for its information content, but living systems must also accommodate the physical properties of such a long molecule," Berndsen said. "Viruses and cells have to deal with the forces involved."

Beyond a clearer understanding of how viruses operate, the approach offers a natural system that is a model for understanding and studying the physics of long polymers like DNA in confined spaces. The insights could also inform biotechnologies that enclose long polymers within minuscule channels and spheres in nanscale devices.

###

Shelley Grimes and Paul Jardine, microbiologists at the University of Minnesota co-authored both papers. Damian delToro, a graduate student in physics at UC San Diego, co-authored the paper published by Physical Review Letters.

The National Science Foundation and the National Institute of General Medical Sciences funded the work.

Doug Smith | Eurek Alert!
Further information:
http://www.ucsd.edu

Further reports about: DNA Relaxation equilibrium knots matter viruses

More articles from Life Sciences:

nachricht Link Discovered between Immune System, Brain Structure and Memory
26.04.2017 | Universität Basel

nachricht Researchers develop eco-friendly, 4-in-1 catalyst
25.04.2017 | Brown University

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

7th International Conference on Crystalline Silicon Photovoltaics in Freiburg on April 3-5, 2017

03.04.2017 | Event News

 
Latest News

From volcano's slope, NASA instrument looks sky high and to the future

27.04.2017 | Earth Sciences

Control of molecular motion by metal-plated 3-D printed plastic pieces

27.04.2017 | Materials Sciences

Move over, Superman! NIST method sees through concrete to detect early-stage corrosion

27.04.2017 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>