title: Formation of the G-quadruplex and i-motif structures in retinoblastoma susceptibility genes (Rb).
abstract: The formation of G-quadruplex and i-motif structures in the 5' end of the retinoblastoma (Rb) gene was examined using chemical modifications, circular dichroism (CD) and fluorescence spectroscopy. It was found that substitutions of 8-methylguanine at positions that show syn conformations in antiparallel G-quadruplexes stabilize the structure in the G-rich strand. The complementary C-rich 18mer forms an i-motif structure, as suggested by CD spectroscopy. Based on the C to T mutation experiments, C bases participated in the C-C+ base pair of the i-motif structure were determined. Experiments of 2-aminopurine (2-AP) substitution reveal that an increase of fluorescence in the G-quadruplex relative to duplex is attributed to unstacked 2-AP within the loop of G-quadruplex. The fluorescence experiments suggest that formation of the G-quadruplex and i-motif can compete with duplex formation. Furthermore, a polymerase arrest assay indicated that formation the G-quadruplex structure in the Rb gene acts as a barrier in DNA synthesis.
authors.affiliation: Department of Chemistry, Graduate School of Science, Kyoto University Sakyo, Kyoto 606-8502, Japan.
authors.forename: Yan
authors.initials: Y
authors.lastname: Xu
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Sugiyama
mesh_terms: D024506:5' Flanking Region; D002942:Circular Dichroism; D003596:Cytosine / Q000737:chemistry; D004247:DNA / Q000096:biosynthesis / Q000737:chemistry*; D054856:G-Quadruplexes; D016161:Genes, Retinoblastoma; D006147:Guanine / Q000031:analogs & derivatives / Q000737:chemistry*; D006801:Humans; D013050:Spectrometry, Fluorescence
chemical_list: C066771:8-methylguanine; D006147:Guanine; D003596:Cytosine; D004247:DNA