A dominant role for DNA secondary structure in forming hypersensitive structures in chromatin

Previous work has suggested that potential information in DNA secondary structure might be used by cells to define DNAase 1- and S1-sensitive chromatin structures associated with promoter and terminator regions. To test this hypothesis, supercoiled pBR322 was cotransfected into L cells. For the majority of transfected clones supercoil-induced S1-sensitive sites in pure pBR322 DNA are also S1-sensitive in L-cell nuclei. These results suggest that the potential of certain DNA sequences to form specific secondary structures in chromatin can be a dominant characteristic. A recombinant chicken beta A-globin supercoiled plasmid was reconstituted in vitro with histones. The reconstituted chromatin also retained the ability to form S1-sensitive sites. Evidence suggests that DNA sequences capable of forming S1-sensitive sites in supercoiled plasmids may bind nucleosomes poorly after reconstitution with histones.