DNA constructs used in the study.
A, retrovirus rv3315 encodes SV40 large T antigen driven by murine embryonic stem cell virus long terminal repeat (LTR) promoter. No antibiotic resistance marker is present. B, plasmid pMA2941 encodes CMV promoter-driven Myc-tagged cre recombinase gene. C, retrovirus rv3441 encodes Moloney murine leukemia virus LTR promoter-driven mitochondrially targeted LIG3. The gene's native MTS and an initiating codon were removed and replaced with MTS from human ornithine transcarbamylase followed by a Myc tag. D, retrovirus rv3491 encodes LTR promoter-driven cre recombinase whose expression is transcriptionally linked (through an internal ribosome entry site, IRES EMV) to the expression of the G418 resistance gene. E, lentivirus lv3380 encodes doxycycline-inducible promoter (TET)-driven mitochondrially targeted LIG3 as in C.