title: Cellular nucleic-acid-binding protein, a transcriptional enhancer of c-Myc, promotes the formation of parallel G-quadruplexes.
abstract: G-rich sequences that contain stretches of tandem guanines can form four-stranded, intramolecular stable DNA structures called G-quadruplexes (termed G4s). Regulation of the equilibrium between single-stranded and G4 DNA in promoter regions is essential for control of gene expression in the cell. G4s are highly stable structures; however, their folding kinetics are slow under physiological conditions. CNBP (cellular nucleic-acid-binding protein) is a nucleic acid chaperone that binds the G4-forming G-rich sequence located within the NHE (nuclease hypersensitivity element) III of the c-Myc proto-oncogene promoter. Several reports have demonstrated that CNBP enhances the transcription of c-Myc in vitro and in vivo; however, none of these reports have assessed the molecular mechanisms responsible for this control. In the present study, by means of Taq polymerase stop assays, electrophoretic mobility-shift assays and CD spectroscopy, we show that CNBP promotes the formation of parallel G4s to the detriment of anti-parallel G4s, and its nucleic acid chaperone activity is required for this effect. These findings are the first to implicate CNBP as a G4-folding modulator and, furthermore, assign CNBP a novel mode-of-action during c-Myc transcriptional regulation.
authors.affiliation: Instituto de Biología Molecular y Celular de Rosario (IBR), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)-Area Biología General, Dpto. de Ciencias Biológicas, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Suipacha 531, S2002LRK Rosario, Argentina.
authors.forename: Mariana
authors.initials: M
authors.lastname: Borgognone
authors.forename: Pablo
authors.initials: P
authors.lastname: Armas
authors.forename: Nora B
authors.initials: NB
authors.lastname: Calcaterra
mesh_terms: D002942:Circular Dichroism; D004277:DNA, Single-Stranded / Q000737:chemistry / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D054856:G-Quadruplexes; D016259:Genes, myc
chemical_list: D004277:DNA, Single-Stranded; D004268:DNA-Binding Proteins