After the ligation, the sample is heated for 5 min at 65°C (Kenzelmann et al., 1999), mixed with 2.5 μl 5 × GLS and run in a single lane on an 8% polyacrylamide gel with a 100-bp ladder as a marker. After staining with SYBR Green I, the gel regions between 600 and 1200 bp are excised and the concatemers are purified as previously described.