Mutagenesis Reveals an Unusual Combination of Guanines in RNA G-Quadruplex Formation.

The classic G-quadruplex motif consists of a continuous array of 3-4 guanine residues with an intermittent loop size of 1-7 nucleotides (G3-4N1-7G3-4N1-7G3-4N1-7G3-4). An RNA G-quadruplex is able to attain only one parallel G-quadruplex topology owing to steric constraints. Investigating the possibilities of the formation of RNA G-quadruplexes with a stretch of sequences deviating from this classic motif will add to the overall conformations of RNA G-quadruplexes, bestowing diversity to this structure. Here, we report unusual combinations of guanine residues involved in RNA G-quadruplex formation in the 5' untranslated region (UTR) of the von Willebrand factor (VWF) mRNA using the mutagenesis approach. Different permutations and combinations of guanine residues form G-quadruplexes. Upon investigation, G-quadruplexes in 5' UTR of VWF mRNA are shown to exhibit an inhibitory function.