RMCE on KH2 cells inserted a cassette that contains a loxP-flanked pgkNEOpolyA cassette, a third loxP site, the tetracycline responsive element (TRE or tetO), the single polycistronic expression cassette 4F2A, SV40 intron plus polyA signal, and a fourth loxP site into the 3'UTR. The 4F2A cassette contains the four mouse reprogramming genes Oct4 (Pou5f1; POU domain, class 5, transcription factor 1), Sox2 (SRY-box containing gene 2), Klf4 (Kruppel-like factor 4 (gut)), and c-Myc (Myc; myelocytomatosis oncogene) separated by three different viral 2A oligopeptides that mediate ribosomal skipping (P2A [from porcine teschovirus-1], T2A [from insect Thosea asigna virus], and E2A [equine rhinitis A virus], respectively).