DNase-sensitive Sites in Nucleosomes. Their Relative Suspectibilities Depend on Nuclease Used

We have used three endonucleases having different catalytic and physicochemical properties to digest HeLa nucleosomes (chromatin core particles) which had been labeled with 32P at their 5'-DNA termini. Each endonuclease nicks nucleosome DNA at the identical sites, supporting the idea that the conformation of the DNA within a nucleosome is the major factor influencing its nuclease susceptibility and indicating that nucleases can indeed yield important information as to nucleoprotein structure. On the other hand, the relaative susceptibility of a given site can differ for each nuclease, indicating that enzyme-substrate interactions unique for each enzyme influence the course of the reaction; this limits the structural information which can be obtained by using a single nuclease to study nucleoprotein structure.