An Intramolecular Triplex Structure From Non-mirror Repeated Sequence Containing BothPy:Pu·Py andPu:Pu·Py Triads

doi:10.1006/jmbi.1994.0041

Journal of Molecular Biology

Volume 245, Issue 5, 3 February 1995, Pages 499-507

https://doi.org/10.1006/jmbi.1994.0041 Get rights and content

Abstract

A plasmid insert containing the (TA)₇GATC(TA)₇inverted repeat and an adjacent (AG)₇tract adopts a cruciform structure at neutral pH. However, under acidic conditions the cruciform becomes readily disrupted in favor of a triplex. The (AG)₇·(CT)₇duplex and one strand of the (TA)₇GATC(TA)₇element are engaged in the three-stranded DNA formation, as determined using single-stranded DNA specific probes. The structure extrudes by displacing the (TA)₇strand adjacent to the (AG)₇, and folding it back into the major groove of the (AG)₇·(CT)₇duplex. This new variant ofH-DNA is supercoil and pH dependent, requiring pH 6.1 or lower to form. The triplex is stabilized by T:A·T and A⁺:G·C triads. This unusual triad composition (50% of T:A·T and 50% of A⁺:G·C), that has not previously been observed in intramolecular triplexes, violates both the widely accepted division of triplexes intoPy:Pu·Py orPu:Pu·Py types and the requirement for mirror repeat symmetry.

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