Figure 1 Estrogen receptor-based artificial gene expression system.(A) Vector constructs of the Gal4-ERT2-VP16 (GEV) expression vector (PB/chEF1α/GEV_Hyg) and gene-of-interest (GOI) expression vectors (PB/UAS/GFP_Zeo and PB/UAS/scFv-Fc_Zeo). PchEF1α, Chinese hamster-derived elongation factor 1α promoter; Gal4-ERT2-VP16 (GEV), estrogen receptor-based artificial transcription factor; Gal4, DNA binding domain of yeast transcription factor; ERT2, ligand binding region of estrogen receptor mutant; PTK, thymidine kinase promoter; Hyg, hygromycin resistance gene; UAS, Gal4-linked upstream activation sequence; Pmin, Ad major late promoter minimal region; GOI, target gene; GFP, green fluorescent protein; anti-prion single-chain antibody fused with the Fc-region of human IgG1 (scFv-Fc); PSV40, SV40 promoter; Zeo, zeocin resistance gene. (B) GEV expressed under a constitutive promoter accumulated in the cytoplasm. In the presence of β-estradiol (E2) or 4-hydroxytamoxifen (4-OHT), GEV translocates into the nucleus and binds to UAS-responsive elements. The activated GEV induces expression of the target gene (scFv-Fc) under control of the UAS/Pmin artificial promoter. Translated scFv-Fc protein is extracellularly secreted.