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.
(3) UMR 218 CNRS/Institut Curie “Nuclear dynamics and genome plasticity”
First time-lapse footage of cell activity during limb regeneration
25.10.2016 | eLife
Phenotype at the push of a button
25.10.2016 | Institut für Pflanzenbiochemie
Ultrafast lasers have introduced new possibilities in engraving ultrafine structures, and scientists are now also investigating how to use them to etch microstructures into thin glass. There are possible applications in analytics (lab on a chip) and especially in electronics and the consumer sector, where great interest has been shown.
This new method was born of a surprising phenomenon: irradiating glass in a particular way with an ultrafast laser has the effect of making the glass up to a...
Terahertz excitation of selected crystal vibrations leads to an effective magnetic field that drives coherent spin motion
Controlling functional properties by light is one of the grand goals in modern condensed matter physics and materials science. A new study now demonstrates how...
Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.
"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...
In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.
A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...
By forcefully embedding two silicon atoms in a diamond matrix, Sandia researchers have demonstrated for the first time on a single chip all the components needed to create a quantum bridge to link quantum computers together.
"People have already built small quantum computers," says Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer...
14.10.2016 | Event News
14.10.2016 | Event News
12.10.2016 | Event News
26.10.2016 | Power and Electrical Engineering
26.10.2016 | Awards Funding
26.10.2016 | Power and Electrical Engineering