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 inSupplementary 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.
For the comparison gel in