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Intramolecular folding in three tandem guanine repeats of human telomeric DNA has been investigated using optical-tweezers, MD simulation and circular dichroism. A mechanically and thermodynamically stable species in this sequence shows a structure consistent with a triplex conformation. A similar species has also been observed to coexist with a(More)
Here we report the analysis of dual G-quadruplexes formed in the four repeats of the consensus sequence from the insulin-linked polymorphic region (ACAGGGGTGTGGGG; ILPR(n)(=4)). Mobilities of ILPR(n)(=4) in nondenaturing gel and circular dichroism (CD) studies confirmed the formation of two intramolecular G-quadruplexes in the sequence. Both CD and single(More)
The insulin linked polymorphism region (ILPR) is known to regulate transcription of the gene coding for insulin. The ILPR has guanine rich segments, suggesting that G quadruplexes may be responsible for this regulatory role. Using mechanical unfolding in a laser tweezers instrument and circular dichroism (CD) spectroscopy, we provide compelling evidence(More)
G-quadruplex has demonstrated its biological functions in vivo. Although G-quadruplex in single-stranded DNA (ssDNA) has been well characterized, investigation of this species in double-stranded DNA (dsDNA) lags behind. Here we use chemical footprinting and laser-tweezers-based single-molecule approaches to demonstrate that a dsDNA fragment found in the(More)
The discovery of G-quadruplexes and other DNA secondary elements has increased the structural diversity of DNA well beyond the ubiquitous double helix. However, it remains to be determined whether tertiary interactions can take place in a DNA complex that contains more than one secondary structure. Using a new data analysis strategy that exploits the(More)
Recent experiments provided controversial observations that either parallel or non-parallel G-quadruplex exists in molecularly crowded buffers that mimic cellular environment. Here, we used laser tweezers to mechanically unfold structures in a human telomeric DNA fragment, 5'-(TTAGGG)4TTA, along three different trajectories. After the end-to-end distance of(More)
Investigation of i-motif is of high importance to fully understand the biological functions of G quadruplexes in the context of double-stranded DNA. Whereas single-molecule approaches have profiled G quadruplexes from a perspective unavailable by bulk techniques, there is a lack of similar literature on the i-motif in the cytosine (C)-rich region(More)
Due to the long-range nature of high-order interactions between distal components in a biomolecule, transition dynamics of tertiary structures is often too complex to profile using conventional methods. Inspired by the exploded view in mechanical drawing, here, we used laser tweezers to mechanically dissect high-order DNA structures into two constituting(More)
Enrichment of four tandem repeats of guanine (G) rich and cytosine (C) rich sequences in functionally important regions of human genome forebodes the biological implications of four-stranded DNA structures, such as G-quadruplex and i-motif, that can form in these sequences. However, there have been few reports on the intramolecular formation of non-B DNA(More)
RNA plays myriad roles in the transmission and regulation of genetic information that are fundamentally constrained by its mechanical properties, including the elasticity and conformational transitions of the double-stranded (dsRNA) form. Although double-stranded DNA (dsDNA) mechanics have been dissected with exquisite precision, much less is known about(More)