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  • Title: Long (dA)n.(dT)n tracts can form intramolecular triplexes under superhelical stress.
    Author: Fox KR.
    Journal: Nucleic Acids Res; 1990 Sep 25; 18(18):5387-91. PubMed ID: 2216711.
    Abstract:
    Plasmids containing long tracts of (dA)n.(dT)n have been prepared and their conformations examined in linear and supercoiled DNA using a series of chemical and enzymic probes which are known to be sensitive to unusual DNA structures. Under superhelical stress and in the presence of magnesium the sequence T69.A69 adopts a conformation at pH 8.0 consistent with the formation of an intramolecular DNA triplex. Site specific cleavage of the supercoiled plasmid by single-strand specific nucleases occurs within the A.T insert; the 5'-end of the purine strand is sensitive to reaction with diethylpyrocarbonate while the central 5-6 bases of the pyrimidine strand are reactive to osmium tetroxide. By contrast shorter inserts of A33.T33 and A23.T23 do not appear to form unusual structures.
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