Intramolecular G-quadruplexes formed by d(GT)12 microsatellite sequence in the presence of K+

Polymorphic d(GT) _n microsatellite sequences are known to dramatically affect the regulation of gene expression. CD spectroscopy, UV melting, fluorescence polarization of ethidium bromide (EtBr), and FRET allowed the detection of a new G-quartet fold formed by the d(GT)₁₂ oligonucleotide in 0.01 M Na-phosphate (pH 8.0) in the presence of 0.1 M KCl. The monomolecular type of the structure was verified by measuring the rotational relaxation time (ρ = 28 ± 0.5 ns) of the EtBr: d(GT)₁₂ complex. CD spectra supported the G-quartet formation. FRET was used to estimate the distance between intercalated EtBr and FITC covalently attached to the 5′ end of d(GT)₁₂ (R ≤ 17 Å). The experimental data agree with the self-folding of d(GT)₁₂ in a G-quartet structure.