Roles of the RGG Domain and RNA Recognition Motif of Nucleolin in G-Quadruplex Stabilization

[Image: see text] G-quadruplexes have important biologic functions that are regulated by G-quadruplex-binding proteins. In particular, G-quadruplex structures are folded or unfolded by their binding proteins and affect transcription and other biologic functions. Here, we investigated the effect of the RNA recognition motif (RRM) and arginine–glycine–glycine repeat (RGG) domain of nucleolin on G-quadruplex formation. Our findings indicate that Phe in the RGG domain of nucleolin is responsible for G-quadruplex binding and folding. Moreover, the RRM of nucleolin potentially binds to a guanine-rich single strand and folds the G-quadruplex with a 5′-terminal and 3′-terminal single strand containing guanine. Our findings contribute to our understanding of how the RRM and RGG domains contribute to G-quadruplex folding and unfolding.