title: [Formation of cruciform structures in pAO3 plasmid DNA on increasing superhelical density].
abstract: The dependence of the crusiciform structure formation on superhelical density was studied by means of high resolution gel-electrophoresis. A short pAO3 DNA plasmid (1683 b. p.) which is a quarter of the ColE1 DNA plasmid and contains the main palindrome of ColE1 DNA was used. The excellent resolution of all topoisomers of pAO3 DNA in gel-electrophoresis made it possible to observe a sharp abruption in the pattern of pAO3 DNA topoisomers separation. The two-dimensional gel-electrophoresis data showed that observed abruption is caused by a sharp decrease of writhing in the molecules with superhelical density--sigma approximately equal to 0,05. An analysis of S1-nuclease digestion products of DNA with different superhelical density was accomplished and these data showed that a sharp structural transition in supercoiled DNA pAO3 is caused by formation of a cruciform structure in the main palindrome.
mesh_terms: D001482:Base Composition; D004262:DNA Restriction Enzymes; D004278:DNA, Superhelical; D004720:Endonucleases; D009690:Nucleic Acid Conformation; D010957:Plasmids; D015719:Single-Strand Specific DNA and RNA Endonucleases
chemical_list: D004278:DNA, Superhelical; D004720:Endonucleases; D004262:DNA Restriction Enzymes; D015719:Single-Strand Specific DNA and RNA Endonucleases
vernacular_title: Obrazovanie krestoobraznykh struktur v DNK plazmidy pAO3 pri uvelichenii sverkhspiral'noĭ plotnosti.