PARENT SESSION
8:00 AM to 8:50 AM
Sunday, April 21, 2002
Refresher Course 5
Radiation Damage to DNA: Structure and Function
Room: Nevada 6-7
Spotheim-Maurizot, Melanie³³Centre de Biophysique Moleculaire, Orleans, France

(RC05) Structural aspects of radiation damage to DNA-protein complexes.

Spotheim-Maurizot, Melanie^*,1, ¹ Centre de Biophysique Moleculaire, CNRS, rue C. Sadron, Orleans, France

ABSTRACT-
Binding of a protein to its cognate DNA sequence is a key step in the regulation of gene expression. If radiation disfavors DNA-protein recognition through the damage of one or of both partners, the whole regulation process may be perturbed. The refresher course will discuss the relation between the radiation damage to a classical model of regulatory systems, the E. coli lactose operator-repressor complex, and the structure of this complex. The complex between a DNA fragment bearing the lactose operator and the repressor is disrupted by exposure to gamma rays. The phenomenon is reversed by the addition of non-irradiated repressors, but not by that of the non-irradiated DNA fragments. Thus, radiation disfavors the DNA-protein recognition primarily by affecting the binding ability of the protein. The dose triggering complex disruption is higher than that inducing the complete loss of binding ability of the repressor irradiated alone. As revealed by calculations of the accessibility of the amino-acids in the complexed and in the free repressor (PDB databank structures) to OH radicals, the protection of the complexed protein is due to : i) the masking of protein's key amino acids by DNA and ii) the binding-induced conformational changes of the protein. In the complex, DNA is protected against radiation damage by the bound protein. Regions with strongly reduced probabilities of strand breakage (footprints) are observed. As revealed by calculations using RADACK, a Monte-Carlo based stochastic model of radiolytic attack, the protection is due to : i) the masking of DNA's specific binding site by the protein and ii) the binding-induced conformational changes of DNA.

KEYWORDS: DNA-protein complexes, radiation-induced damage to DNA and proteins, DNA and protein strucure