Detecting the DNA kinks in a DNA-CRP complex in solution with iodine-125 radioprobing

Auger-electron-emitting radioisotopes such as I-125 produce DNA strand brea ks within nanometer range of the decay site. Here we analyze these breaks i n order to study changes in DNA conformation upon binding with cyclic AMP r eceptor protein (CRP) in solution. The clear difference we found in break f requency in the CRP-DNA complex, as compared to the naked DNA duplex, corre lates with the increased distances between the deoxyriboses and the radioio dine atom caused by the CRP-induced kink observed in the cocrystal. Thus, w e demonstrate that I-125 radioprobing can be used to study fine conformatio nal changes of DNA within DNA-protein complexes.