Twisting DNA into a plectoneme
Marc Emanuel
Instituut-Lorentz for theoretical physics, Leiden university
Lundi 01/03/2010, 14:00
Salle Claude Itzykson, Bât. 774, Orme des Merisiers

Due to the chiral nature of DNA, torsion is an important instrument the cell uses to regulate the accessibility of the genetic code. The amount of local twist that can be reached by increasing the torque depends, to large extend, on the ease with which this torque can create a plectoneme. This supercoiling of DNA has been studied extensively in the past in the context of the compaction of DNA in bacteria. With the onset of single molecule experiments using magnetic or optical beads, controlled experiments have been performed to investigate the plectoneme formation under varying ionic conditions. On the theoretical front, a full understanding of the physics involved has been lacking. Most models take a phenomenological approach, with some limited physical input. \par We have managed to explain the data starting from the independently known properties of DNA without any adjustable parameters. I will show how an intricate balance between elasticity, electrostatics and thermal fluctuations sets the formation of plectonemes over a wide range of forces, torques, lengths and salt concentrations revealing some unexpected features on the way.

Contact : Gregoire MISGUICH


Retour en haut