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SUMMARY:Chiral effects in DNA supercoiling - Cortini\, R (Imperial College
  London)
DTSTART:20120905T105000Z
DTEND:20120905T111000Z
UID:TALK39543@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:Supercoiling is a topological property of DNA which is known t
 o be crucially important in the genetic regulation of virtually every livi
 ng cell. Electrostatic interactions play a fundamental role in determining
  the conformation of DNA molecules. They are generally taken into account 
 assuming that the charge is homogeneously smeared on the surface of DNA mo
 lecules. We developed a theory that instead takes into account the helical
  pattern of charge on the DNA molecular surfaces. We find that the intrins
 ic chirality of the charge structures gives rise to important and non triv
 ial phenomena. Crucially\, it determines an asymmetry in the energetics of
  DNA-DNA crossovers: right-handed crossings\, occurring in positively supe
 rcoiled molecules are more stable than left-handed ones\, which occur in n
 egatively supercoiled molecules. We explored the consequences of this fact
  first by developing a theory of spontaneous DNA braid formation\, and the
 n applying it to closed loop DNA supercoilin g and single-molecule DNA mic
 romanipulation experiments. The theory can give an account of some yet une
 xplained observations and biological facts. It gives a plausible explanati
 on for the occurrence of tight supercoiling of DNA loops observed in cryo-
 EM and AFM images in high ionic strength environment. It can shed light on
  the preference for positive supercoiling in hyperthermophylic bacteria an
 d archea. Finally\, it induces to reinterpret classical experiments that s
 how that divalent metal ions overwind DNA. The biological implications of 
 these important facts could be very important\, and are yet to be fully ex
 plored. \n
LOCATION:Seminar Room 1\, Newton Institute
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