Poly a poly u

ctDNA and poly A-poly U were purchased from Sigma-Aldrich (Merck, Europe) and used without further purification. The stock solution was prepared by dissolved a small portion of the lyophilized polynucleotide in 200 μL of NaCac 50 mM buffer and stored at 5 °C overnight. The concentration of the stock solution was checked by measuring the absorption of four accumulative additions of the stock solution to a 1 mL of NaCac 50 mM. Concentration was then calculated by using the molar extinction coefficient given by the supplier (6600 M⁻¹ cm⁻¹ for ctDNA and 6000 M⁻¹ cm⁻¹ for poly A-poly U). Stock solutions were maintained at −10 °C and defrost before use. Ethidium bromide (EB) (3,8-diamino-5-ethyl-6-phenylphenanthridinium bromide) and DAPI (2-(4-amidinophenyl)-6-indolecarbamidine dihydrochloride, 4′,6-diamidino-2-phenylindole dihydrochloride) were purchased from commercial sources and used without further purification.

Polynucleotides were purchased as follows: polyG–polyC, polyA–polyU (Sigma-Aldrich, St. Louis, MO), calf thymus ctDNA (Aldrich). Polynucleotides were dissolved in PBS buffer, I =  0.05 mol dm⁻³, pH 7.0. The calf thymus ctDNA was additionally sonicated and filtered through a 0.45 mm filter. The polynucleotide concentration was spectroscopically determined as the concentration of nucleobases⁶².

Chemicals for synthesis: 4-(1-pyrenyl)butyric acid (Alfa Aesar, 97%), triethylamine (Et₃N) (Sigma Aldrich, 99%), hydroxybenzotriazole (HOBt) (Sigma Aldrich, 97%), 2-(1H-benzotriazole-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate (HBTU) (Alfa Aesar, 98%), Silica gel 60, PF₂₅₄ for preparative thin layer chromatography (Merck).
Nucleotides (AMP, GMP, UMP and CMP) were purchased from Sigma, dissolved in stock solutions of c = 0.01 M and used. Polynucleotides were purchased as noted: poly dAdT–poly dAdT, poly A–poly U, poly dGdC–poly dGdC, (Sigma), calf thymus (ct)-DNA (Aldrich) and dissolved in sodium cacodylate buffer (I = 0.05 M, pH = 7.0), as described by producer. The presence of double stranded helix was confirmed by single, well-defined transition in the thermal denaturation experiment, giving T_m value agreeing well with the literature; as well as by collecting CD spectra of free ds-DNA or ds-RNA, which also agreed well with the literature.^{48,49 (link)} The ct-DNA was additionally sonicated and filtered through a 0.45 mm filter to obtain mostly short (ca. 100 base pairs) rod-like B-helical DNA fragments. Polynucleotide concentration was determined spectroscopically as the concentration of phosphates (corresponds to c(nucleobase)).⁵²