A2UCOE gives rise to stable eGFP expression in P19 cells compared to SFFV and EF1α regulatory elements. (a) Schematic of the lentiviral transfer vectors used in the study. The transcription direction of CBX3-HNRPA2B1 within A2UCOE is indicated. LTR, long-terminal repeat; RRE, rev-response element; ψ, packaging signal. (b) P19 cells were transduced with vectors shown in a, at multiplicity of infection (MOI) of 5 for EF1α and A2UCOE, and MOI 10 for SFFV. eGFP expression was assessed by flow cytometry at different time points after transduction up to 44 days, as indicated. The underlined numbers shown above each bar represent mean fluorescence intensity (MFI). Italicized numbers denote vector copy number per cell determined by Q-PCR. Note: Unlike SFFV and EF1α, eGFP expression driven from A2UCOE is stable throughout the culture period. This is achieved with a low vector copy number of one per cell compared to the high vector copy numbers present for EF1α and SFFV.