As one kind of non-canonical structures of nucleic acid, G-quadruplexes (G4) exist universally in the genome of different organisms and in humans. G4 are supposed to play crucial regulatory roles in gene replication, translation and expression. Therefore, G4s are handled as a promising target for chemo-therapy. A number of small molecules have been designed as specific G4-binders and to interfere with their normal function in vivo. To date, most studies concentrated on DNA G4s, while the understanding of RNA G4s is far from comprehensive.
In our group, we explore the structural details of RNA G4s and their interactions with metal ions and metal complexes by NMR and crystallography. We expanded our recent attempts by applying photophysical methods, such as fluorescence spectroscopy, including lifetime and dynamic anisotropy, to investigate the interaction of G4 with fluorescent metal complexes. G4 under investigation comprise the TERRA, NRAS and BCL2 RNAs.
 Sebastian L.B. König, Julian L. Huppert, Roland K.O. Sigel RKO, Amanda C. Evans*, Nucleic Acid Res., 2013, 41(15), 7453–7461.
 Helena Guiset Miserachs, Daniela Donghi, Richard Börner*, Silke Johannsen*, Roland K. O. Sigel*, J. Biol. Inorg. Chem., 2016, 21, 975-986.
 Qian Cao, Yi Li, Eva Freisinger, Peter Z. Qin*, Roland K. O. Sigel*, Zong-Wan Mao*, Inorg. Chem. Front., 2017, 4, 10-32.