Endogenous ELM 5 and MEL/ELM promoters expressing reporter gene activity in transfected ELM cells.

ELM VL30 promoters were isolated, confirmed, and quantified for their epo responsiveness20 and cloned into the LTRs of the expression vector, VLIBAG (A). Mass cultures of ELM transfectants carrying the endogenously expressed promoters MEL/ELM (B) and ELM 5 (C) within the heterologous cassette, VLIBAG, were histochemically stained with X-gal after 2 weeks of selective growth conditions. The unexpressive negative control transfectant, VLIBAG, with the NVL3 promoter is shown (D) as well as the positive control RVBAG retroviral vector (E). Original magnification, × 200 (B-E).