Tbe urea page gel

After extension, for internal quality control, the lengths of the concatemers were evaluated by diluting 1 μl of in vitro reaction with 19 μl water. For quality control, samples were then run on 1–2% E-Gel EX agarose gels (Thermo Fisher #G402001) for 10 min on the E-gel apparatus (Invitrogen, iBase) alongside a 1 kb Plus DNA Ladder (Invitrogen) and imaged with the SybrGold channel on a Typhoon FLA 9000 scanner.
For the comparison gel in Supplementary Fig. 6, unpurified concatemers were run using 6% TBE-UREA PAGE gels (Thermo Fisher) at 55°C. The gel was pre-run for 1 h before loading the samples. 160 ng Quick-Load Purple Low Molecular Weight DNA Ladder (NEB #N0557S) was loaded as size reference. The reaction products were diluted 1:7 with 2× Urea-Loading Dye, and denatured at 95°C for 5 min. 9 μl from each sample was loaded on the gel. Both samples and the ladder were denatured. Samples were run for 20 min at 75 V, and at 130 V for 1 h. Gels were stained with 1:10,000 SybrGold in 0.5× Tris-Borate-EDTA (TBE) for 30 min and scanned on a Typhoon FLA 9000 scanner.

DNA templates for Nucleolin-bound regions were PCR amplified or chemically synthesized by Integrated DNA Technologies and in-vitro transcribed with MEGAshortscript T7 transcription kit (Thermo Fisher Scientific). In-vitro transcribed products and chemically synthesized 5’-tRF^Cys (Integrated DNA Technologies) were purified on a 10% TBE-Urea PAGE gel (Thermo Fisher Scientific) before dephosphorylated with Quick CIP (New England Biolabs) and 5’ radiolabeled using T4 PNK (New England Biolabs). Labeling reactions were purified with acid-phenol chloroform and chloroform before overnight precipitation with ethanol supplemented with 200 mM NaCl and glycogen.