A CRE-Activated Transgene. A) An illustration of the Cre-activated transgene vector. The full vector, pTC-loxPTK-G, produces PTK from the mini-CAGs promoter. Transcriptional leakage into the downstream gene, GFP, is limited due to the incorporation of three full poly-adenylation signals, a so-called triple-stop. Recombination by Cre eliminates PTK and triple-stop, activating GFP expression from pTC-lox-G. B) pTC-loxPTK-G was transfected into PEGE cells with (+Cre) or without (-Cre) pPGK-nlsCre. Cells were monitored for GFP expression by fluorescent microscopy (image inserts) and flow cytometry. The percentage of cells expressing GFP was dependent on co-transfection with pPGK-nlsCre. C) PEGE cells were transfected with pTC-loxPTK-G along with pPGK-nlsCre (+Cre), pCMV-β (+βgal), pKUb-SB11 (+SB), or pKUb-SB11 and pPGK-nlsCre (+SB +Cre). The cells were plated in puromycin selective media and colonies were counted.