Schematic representation of the retrovirus vectors used in this study.

LTR indicates long terminal repeat; ψ, packaging signal;hTERT, human telomerase catalytic subunit; SV40E, SV40 minimal early promoter; hygro, hygromycin-resistant gene;ras, H-ras; puro, puromycin-resistant gene; tsT, SV40 large T antigen; IRES, internal ribosome entry site; and neo, neo phosphotransferase gene.