mammalian expression vector pCEP4 (Invitrogen) was modified to possess a
2nd or 3rd Generation Tet-inducible promoter
(ClonTech) by Gibson assembly. LINE-1 sequences were inserted into the
vector backbone by Gibson assembly with PCR amplicons of endogenous LINE-1
sequence (LINE-1 RP) or ORFeus codon-optimized sequence83 . Control pCEP4 vectors encoded
either eGFP or lacked expression inserts. LINE-1 point mutant constructs
were also created by amplification and Gibson assembly. For sleeping-beauty
integrated LINE-1, ORFeus codon-optimized LINE-1 was cloned into the donor
vector pSBtet-RN or pSBtet-GN84 by Gibson assembly. Briefly, pSBtet-RN or GN was
digested with SfiI and DraIII, gel purified and assembled with PCR-amplified
LINE-1 (primers SB-ORFeus-5 and SB-ORFeus-3 in
the HiFi 2X Assembly Master Mix (NEB, Ipswich, MA).