title: Propeller-type parallel-stranded G-quadruplexes in the human c-myc promoter.
abstract: The nuclease-hypersensitivity element III1 in the c-myc promoter is a good anticancer target since it largely controls transcriptional activation of the important c-myc oncogene. Recently, the guanine-rich strand of this element has been shown to form an equilibrium between G-quadruplex structures built from two different sets of G-stretches; two models of intramolecular fold-back antiparallel-stranded G-quadruplexes, called "basket" and "chair" forms, were proposed. Here, we show by NMR that two sequences containing these two sets of G-stretches form intramolecular propeller-type parallel-stranded G-quadruplexes in K(+)-containing solution. The two structures involve a core of three stacked G-tetrads formed by four parallel G-stretches with all anti guanines and three double-chain-reversal loops bridging three G-tetrad layers. The central loop contains two or six residues, while the two other loops contain only one residue.
authors.affiliation: Structural Biology Program, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA. phantuan@mskcc.org
authors.forename: Anh Tuân
authors.initials: AT
authors.lastname: Phan
authors.forename: Yasha S
authors.initials: YS
authors.lastname: Modi
authors.forename: Dinshaw J
authors.initials: DJ
authors.lastname: Patel
mesh_terms: D004247:DNA / Q000737:chemistry*; D016259:Genes, myc / Q000235:genetics*; D006147:Guanine / Q000737:chemistry; D006801:Humans; D008957:Models, Genetic; D009690:Nucleic Acid Conformation; D011401:Promoter Regions, Genetic / Q000235:genetics*; D014158:Transcription, Genetic / Q000235:genetics
chemical_list: D006147:Guanine; D004247:DNA