Cruciform extrusion facilitates intramolecular triplex formation between distal oligopurine.oligopyrimidine tracts: long range effects. |
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Authors: | J Klysik |
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Institution: | Department of Biochemistry, School of Medicine, University of Alabama, Birmingham 35294. |
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Abstract: | Two short d(AG)n tracts separated by either of two 40-base pair (bp) inverted repeats adopt a triple-stranded conformation (H-DNA) at the bottom of an extruded cruciform stem in negatively supercoiled plasmids at pH 4.5. Plasmids containing one d(AG)n adjacent to the inverted repeat or containing two d(AG)n tracts separated by a random sequence did not form the triplex structures. These conclusions were derived from chemical modification patterns and UV-sensitivity studies. Two-dimensional agarose gel electrophoresis revealed that the entire insert containing the cruciform and the triplex is locally unlinked. Moreover, a long range structural effect (over 40 bp of random sequence) of one (AG)7 block on the behavior of a second (AG)7 sequence was detected. This effect cannot be transmitted throughout a 50-bp segment of random sequence. A GenBank search revealed the frequent occurrence of short oligopurine blocks with an intervening random sequence of 17-40 bp. |
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