A structural transition in d(AT)n.d(AT)n inserts within superhelical DNA.
We have constructed plasmids carrying d(AT)n.d(AT)n inserts of different lengths. Two-dimensional gel electrophoresis patterns show that an increase in the negative superhelicity of these DNAs brings about a structural transition within the inserts, resulting in a reduction of the superhelical stress. However, this reduction corresponds to the expected values neither for cruciform nor the Z form. Those DNA topoisomers in which the structural transition had occurred proved to be specifically recognizable by single-strand-specific endonuclease S1, with the cleavage site situated at the centre of the insert. These data, as well as kinetic studies, suggest that the cloned d(AT)n.d(AT)n sequences adopt a cruciform rather than the Z-form structure. We discuss plausible reasons of the discrepancy between the observed superhelical stress release and that expected for the transition of the insert to the cruciform state.
D001483:Base Sequence; D003035:Cobalt / Q000494:pharmacology; D004278:DNA, Superhelical; D015180:Electrophoresis, Gel, Two-Dimensional; D004926:Escherichia coli / Q000235:genetics; D007700:Kinetics; D009690:Nucleic Acid Conformation / Q000187:drug effects; D010957:Plasmids; D011067:Poly dA-dT; D011089:Polydeoxyribonucleotides; D015183:Restriction Mapping; D015719:Single-Strand Specific DNA and RNA Endonucleases; D014169:Transformation, Bacterial
D004278:DNA, Superhelical; D011089:Polydeoxyribonucleotides; D011067:Poly dA-dT; D003035:Cobalt; D015719:Single-Strand Specific DNA and RNA Endonucleases