Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Biophysics : When chromosomes stretch

27.04.2006
Biophysicists at the Institut Curie/CNRS, in collaboration with CNRS and University Pierre et Marie Curie physicists and biologists, have just demonstrated the remarkable elasticity of chromatin, the DNA-protein complex that makes up the chromosomes.

Observed by nanomanipulation of individual DNA molecules, this resilience facilitates the work of the enzymes that “read” the genetic material and of those that repair it if damaged. When alterations – mutations – remain in the DNA, there is a risk that defective, even tumor cells may arise. The elasticity of chromatin is therefore of crucial importance in the life of the cell.

The genetic material has clearly not yet divulged all its secrets. Hitherto, only its chemical composition and spatial organization were taken into account. The role of the physical properties of DNA, such as its mechanical response to torsion, is now beginning to be understood. These discoveries were published in the May 2006 issue of Nature Structural & Molecular Biology.

Each of our cells contains all the information needed for correct functioning of the body. This information, which directs the synthesis of all proteins, is written in the DNA in the form of a genetic code, a “book” of huge complexity containing some three thousand million letters. The spatial organization of this genetic code in the nucleus is not random: in addition to the information contained in the genetic code, there is also information implicit in the three-dimensional arrangement of the genetic material. So, the reading and expression of DNA depend on both the genetic code and how it is organized spatially. Any error in this ultrasophisticated arrangement can lead to disorganization of the genome, changes in gene expression, and cellular dysfunction.

Chromatin limbers up

The highly ordered organization of DNA (see box) is based first and foremost on histones(1). The DNA double helix wraps around these "condensing" proteins to form a bead necklace – chromatin. By varying the condensation, it is possible to modulate how accessible DNA is to proteins, thereby influencing its transcription, repair and so forth. In particular, chromatin organization is involved in the regulation of gene expression.

At the Institut Curie, the CNRS team of Jean-Louis Viovy(2), MMBM began to be interested in chromatin condensation during a collaboration with the group of Geneviève Almouzni(3), a specialist in the field. The MMBM group is now investigating in depth the mechanics of chromatin dynamics in collaboration with the biologists of Ariel Prunell’s team at the Institut Jacques Monod, Jean-Marc Victor’s group of theoreticians at the University Paris VI, and Vincent Croquette’s team at the Ecole Normale Supérieure in Paris.

By using “molecular adhesive tape”, a bead a few microns across is attached to one end of the DNA. This bead can be observed under the microscope, and so the position of the end of the DNA can be deduced. The other end of the DNA is attached to the wall of a recipient. Using magnets, a force is applied to the bead, thereby stretching the DNA molecule.

Using these “magnetic tweezers”, it is possible to hold the ends of an individual DNA fiber and apply torsion and forces comparable to those exerted by biological molecules. This experiment demonstrated that the chromatin fiber is extremely flexible in torsion and can be twisted clockwise and anticlockwise without changing its length. This plasticity, which is five times greater than that of naked DNA, can be explained by a theoretical model in which there is a state of equilibrium between three different configurations of the nucleosomes.

This great flexibility of the DNA bead necklace is vital for the cell’s functions. In particular, it enables the chromatin fiber to withstand the twisting forces exerted by the enzymes in charge of DNA transcription, without being damaged, and without the need for other proteins. Because of its flexibility, the chromatin fiber transmits the resulting structural changes as “information” on how these enzymes work.

In conclusion, the flexibility of the chromatin fiber facilitates and accelerates DNA’s reaction to changes in its environment. This flexibility plays a vital role in the regulation of gene expression and in cellular functions. Only biophysical approaches on the scale of a single DNA molecule can yield such observations, which are indispensable to a better and multifaceted understanding of DNA, its interactions and cell function.

(1) DNA wraps around small proteins called histones, which provide information in addition to the genetic code: the so-called "histone code". Histones have been highly conserved through evolution and are most abundant in the cell nucleus. Each cell contains some 60 million histones, which together constitute a mass close to that of the genetic material.
(2) “Macromolecules and Microsystems in Biology and Medicine” group in UMR 168 CNRS/Institut Curie “Curie Physical Chemistry”

(3) UMR 218 CNRS/Institut Curie “Nuclear dynamics and genome plasticity”

Catherine Goupillon | alfa
Further information:
http://www.curie.fr
http://www.nature.com/nsmb/index.html

More articles from Life Sciences:

nachricht Decoding the genome's cryptic language
27.02.2017 | University of California - San Diego

nachricht New risk factors for anxiety disorders
24.02.2017 | Julius-Maximilians-Universität Würzburg

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Safe glide at total engine failure with ELA-inside

On January 15, 2009, Chesley B. Sullenberger was celebrated world-wide: after the two engines had failed due to bird strike, he and his flight crew succeeded after a glide flight with an Airbus A320 in ditching on the Hudson River. All 155 people on board were saved.

On January 15, 2009, Chesley B. Sullenberger was celebrated world-wide: after the two engines had failed due to bird strike, he and his flight crew succeeded...

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

New pop-up strategy inspired by cuts, not folds

27.02.2017 | Materials Sciences

Sandia uses confined nanoparticles to improve hydrogen storage materials performance

27.02.2017 | Interdisciplinary Research

Decoding the genome's cryptic language

27.02.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>