title: Triple rings: a new type of compact structure of circular DNA.
abstract: Complexes of circular superhelical pBR322 DNA with a synthetic tripeptide capable of beta-structure formation (dansylhydrazide trivaline) were studied at different peptide/DNA ratios by electron microscopy. It was shown on rotary-shadowed preparations that peptide binding induces intramolecular DNA condensation and compact ring-shaped particles are formed from fibres 120 A thick. The analysis of the morphology of the ring structures observed at various peptide/DNA ratios as well as contour length measurements enabled us to draw conclusions about the organization of the double-stranded DNA filaments in these structures. It was established that the fibres forming compact rings contain three double-stranded DNA segments closely associated due to DNA-peptide and peptide-peptide interactions. The mechanisms leading to the formation of the triple rings may be important in DNA condensation in vivo.
mesh_terms: D004270:DNA, Circular; D004278:DNA, Superhelical; D046911:Macromolecular Substances; D008854:Microscopy, Electron; D009842:Oligopeptides; D010957:Plasmids
chemical_list: D004270:DNA, Circular; D004278:DNA, Superhelical; D046911:Macromolecular Substances; D009842:Oligopeptides; C025780:dansylhydrazide trivaline