title: Intra- and interloop interactions in the folded G quartet structure of Oxytricha telomeric sequence.
abstract: The antiparallel intramolecular G quartet structure for the 3.5 copy Oxytricha telomeric sequence d(G4T4)3G4 has been established using a combination of spectroscopic and chemical probing methods. In the presence of Na+ ions, this sequence exhibits a circular dichroism spectrum with a positive band at 295 nm and a negative band around 265 nm, characteristic of an antiparallel G quartet structure. Further, we show that d(G4T4)3G4 adopts an antiparallel intramolecular G quartet structure even in K+ unlike d(G4T4G4). KMnO4 probing experiments indicated the existence of intra and interloop interactions in the Na+ induced structure. We have found that K+ not only increases the thermal stability of G quartet structure but also binds to the loop region and disrupts stacking and interloop interactions. Biological consequences of such cation-dependent conformational micro-heterogeneity in the loop region of G quartet structures is also discussed.
authors.affiliation: Molecular Biophysics Unit, Indian Institute of Science, Bangalore, India.
authors.forename: P
authors.initials: P
authors.lastname: Balagurumoorthy
authors.forename: S K
authors.initials: SK
authors.lastname: Brahmachari
mesh_terms: D000818:Animals; D001483:Base Sequence; D006147:Guanine / Q000737:chemistry*; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D016813:Oxytricha / Q000235:genetics*; D016615:Telomere / Q000737:chemistry*
chemical_list: D006147:Guanine