title: Direct experimental evidence for quadruplex-quadruplex interaction within the human ILPR.
abstract: 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 molecule studies using optical tweezers showed that the two quadruplexes in the ILPR(n)(=4) most likely adopt a hybrid G-quadruplex structure that was entirely different from the mixture of parallel and antiparallel conformers previously observed in the single G-quadruplex forming sequence (ILPR(n)(=2)). These results indicate that the structural knowledge of a single G-quadruplex cannot be automatically extrapolated to predict the conformation of multiple quadruplexes in tandem. Furthermore, mechanical pulling of the ILPR(n)(=4) at the single molecule level suggests that the two quadruplexes are unfolded cooperatively, perhaps due to a quadruplex-quadruplex interaction (QQI) between them. Additional evidence for the QQI was provided by DMS footprinting on the ILPR(n)(=4) that identified specific guanines only protected in the presence of a neighboring G-quadruplex. There have been very few experimental reports on multiple G-quadruplex-forming sequences and this report provides direct experimental evidence for the existence of a QQI between two contiguous G-quadruplexes in the ILPR.
authors.affiliation: Department of Chemistry, School of Biomedical Sciences, Kent State University, Kent, OH 44242, USA.
authors.forename: Joseph D
authors.initials: JD
authors.lastname: Schonhoft
authors.forename: Rabindra
authors.initials: R
authors.lastname: Bajracharya
authors.forename: Soma
authors.initials: S
authors.lastname: Dhakal
authors.forename: Zhongbo
authors.initials: Z
authors.lastname: Yu
authors.forename: Hanbin
authors.initials: H
authors.lastname: Mao
authors.forename: Soumitra
authors.initials: S
authors.lastname: Basu