Assessing DNA Structures with 125I Radioprobing

Iodine-125 radioprobing is based on incorporation of radioiodine into a defined position in a nucleic acid molecule. Decay of 125I results in emission of multiple low energy Auger electrons that, along with positively charged residual daughter nuclide, produce DNA strand breaks. The probability of such strand breaks at a given nucleotide is in reverse proportion to the distance from the 125I atom to the sugar of that nucleotide. Therefore, conclusions can be drawn about the conformation or folding of a DNA or RNA molecule base on the distribution of 125I decay-induced strand breaks. Here we describe in detail an application 125I radioprobing to study the conformation of quadruplex structures, and discuss the advantages and limitations of the method.