Investigation of possible G-quadruplex formation by GU- and GA-rich repeats and their role in translation

RNA G-quadruplexes (rG4s) are involved in many aspects of cellular and viral protein expression. rG4s consist of at least two stacks of guanine tetrads that are stabilized by non-Watson-Crick-Franklin base pairs. It is currently unknown how single or multiple non-G nucleotide insertions affect the stability or function of rG4s. Here, we investigated the G4-forming potential of GU- and GA-rich sequences by measuring their ability to inhibit ribosomal scanning and induce -1 ribosomal frameshifting (-1 FS) using a cell-free lysate. Our results show that, in contrast to canonical rG4s, GU and GA repeats with eight or more guanines do not affect ribosomal scanning or stimulate -1 FS. However, in the presence of G4-stabilizing ligands PhenDC3 or pyridostatin, GU and GA repeats strongly inhibited scanning and induced -1 FS. These findings have implications for the structural landscape of rG4s and the potential side-effects of G4 targeting drugs in general.