Single-molecule manipulation of TERRA G-quadruplexes by optical tweezers. Left, three-dimensional illustration of the experimental set-up and, right, a typical force-extension curve of the biomolecular system, where an unfolding and a refolding event (blue and green curves, respectively) of a single G-quadruplex takes place.
Gutierrez I, Garavis M, de Lorenzo S, Villasante A, Gonzalez C, Arias-Gonzalez JR.
J Phys Chem Lett2018 May; 9: 2498.
TERRA is an RNA molecule transcribed from human subtelomeric regions toward chromosome ends potentially involved in regulation of heterochromatin stability, semiconservative replication, and telomerase inhibition, among others. TERRA contains tandem repeats of the sequence GGGUUA, with a strong tendency to fold into a four-stranded arrangement known as a parallel G-quadruplex. Here, we demonstrate by using single-molecule force spectroscopy that this potential is limited by the inherent capacity of RNA to self-associate randomly and further condense into entropically more favorable structures. We stretched RNA constructions with more than four and less than eight hexanucleotide repeats, thus unable to form several G-quadruplexes in tandem, flanked by non-G-rich overhangs of random sequence by optical tweezers on a one by one basis. We found that condensed RNA stochastically blocks G-quadruplex folding pathways with a near 20% probability, a behavior that is not found in DNA analogous molecules.