Structural polymorphism in DNA

We have used the enzyme micrococcal nuclease and the methylating reagent dimethyl sulfate to examine the structural properties of eukaryotic DNAs. Our studies demonstrate extensive structural polymorphism in the DNA double helix. Moreover, we find that the distribution of helical variants is in some instances correlated with the functional organization of the DNA. These observations raise the possibility that eukaryotic DNAs may be organized into discrete functional units having characteristic structural properties. In addition, we find that boundaries between different functional units are typically marked by DNA segments having unusual conformational properties. Such structural perturbations could serve as signals in the utilization of genetic information in eukaryotes, and may be important in a variety of different protein-DNA interactions.