Strand-Biased Formation of G-Quadruplexes in DNA Duplexes Transcribed with T7 RNA Polymerase.

G-quadruplex-forming sequences are enriched near transcription start sites (TSSs) in animal genes. They readily form G-quadruplexes in transcription, which in turn regulate transcription. Therefore, the control of G-quadruplex formation is important for their functionality.

A competitive formation of DNA:RNA hybrid G-quadruplex is responsible to the mitochondrial transcription termination at the DNA replication priming site.

Human mitochondrial DNA contains a distinctive guanine-rich motif denoted conserved sequence block II (CSB II) that stops RNA transcription, producing prematurely terminated transcripts to prime mitochondrial DNA replication. Recently, we reported a general phenomenon that DNA:RNA hybrid G-quadruplexes (HQs) readily form during transcription when the non-template DNA strand is guanine-rich and such HQs in turn regulate transcription. In this work, we show that transcription of mitochondrial DNA leads to the formation of a stable HQ or alternatively an unstable intramolecular DNA G-quadruplex (DQ) at the CSB II.

Co-transcriptional formation of DNA:RNA hybrid G-quadruplex and potential function as constitutional cis element for transcription control.

G-quadruplex formation in genomic DNA is considered to regulate transcription. Previous investigations almost exclusively focused on intramolecular G-quadruplexes formed by DNA carrying four or more G-tracts, and structure formation has rarely been studied in physiologically relevant processes. Here, we report an almost entirely neglected, but actually much more prevalent form of G-quadruplexes, DNA:RNA hybrid G-quadruplexes (HQ) that forms in transcription.

Contribution of telomere G-quadruplex stabilization to the inhibition of telomerase-mediated telomere extension by chemical ligands.

Inhibition of telomerase activity through stabilizing telomere G-quadruplex with small chemical ligands is emerging as a novel strategy for cancer therapy. For the large number of ligands that have been reported to inhibit telomerase activity, it is difficult to validate the contribution of G-quadruplex stabilization to the overall inhibition. Using a modified telomere repeat amplification protocol (TRAP) method to differentiate the telomere G-quadruplex independent effect from dependent ones, we analyzed several ligands that have high affinity and/or selectivity to telomere G-quadruplex.

Kinetic and thermodynamic control of G-quadruplex folding.

A matter of speed: when allowed to fold in a K(+)/poly(ethylene glycol) solution, the guanine (G)-rich strand of vertebrate telomere DNA forms a parallel/antiparallel G-quadruplex, which is a (3+1) hybrid, within microseconds before slowly transforming into the parallel one within hours. Thus, the conformation that a G-quadruplex initially adopts under physiological conditions may not be the one it adopts at the equilibrium state.

G-quadruplex formation at the 3' end of telomere DNA inhibits its extension by telomerase, polymerase and unwinding by helicase.

Telomere G-quadruplex is emerging as a promising anti-cancer target due to its inhibition to telomerase, an enzyme expressed in more than 85% tumors. Telomerase-mediated telomere extension and some other reactions require a free 3' telomere end in single-stranded form. G-quadruplex formation near the 3' end of telomere DNA can leave a 3' single-stranded tail of various sizes.

G-quadruplex hinders translocation of BLM helicase on DNA: a real-time fluorescence spectroscopic unwinding study and comparison with duplex substrates.

Sequences with the potential to form G-quadruplex structures are spread throughout genomic DNA. G-quadruplexes in promoter regions can play regulatory roles in gene expression. Expression of protein-encoding genes involves processing of DNA and RNA molecules at the level of transcription and translation, respectively.