Excision activity upon CpG methylation. CpG-methylated or untreated donor plasmids were co-transfected with/without a helper plasmid; 48 h post-transfection plasmids were extracted, purified and DNA amounts were normalized. After two rounds of nested PCR, the product band intensity represents the relative efficiency of transposon excision. (A) Excision activity of different TEs in HeLa cells. Upper panel: Dilutions of PCR input DNA for quantification of FP excision. (B) Excision of SB in different HCT116 knockout cell lines. (C) SB excision in HCT116 Dnmt3b knockout cells. Increasing amounts of aza-deoxycytidine (aza-dC) block de novo CpG methylation. aza-dC: aza-deoxycytidine; FP: Frog Prince; SB: Sleeping Beauty; PCR: polymerase chain reaction; TE: transposable element.