Purification and Characterization of Telomeric DNA

pSXneo(T2AG3) plasmid DNA containing 270 TTAGGG repeats was purchased from Addgene and was purified from Stbl2 cells (Invitrogen)52 (link). To generate linear DNA fragments containing TTAGGG repeats (T270) for AFM imaging, digestion of pSXneo(T2AG3) plasmid DNA (10 μg) was carried out at 37 °C for 4 hr using HpaI (130 U, NEB). The final digested product was purified using the QIAquick PCR Purification Kit (Qiagen). The electrophoresis mobility shift assays (EMSAs) were carried out as reported previously using an Alexa488 labeled 48-bp duplex DNA susbrate containing 3 TTAGGG repeats (Top strand: 5′[Alexa488]TTAGGGTTAGGGTTAGGGATGTCCAGCAAGCCAGAATTCGGCAGCGTA-3′)50 (link). The DNA substrate containing a mismatch was prepared as described previously51 (link)53 (link).