ABCG2 is sufficient to generate the SP profile in 293 cells.

(A) Illustration of the bicistronic vectors used to transfect 293 cells. CMV indicates cytomegalovirus immediate early promoter/enhancer; MCS, multiple cloning site; and IRES, internal ribosomal entry site. (B,E) Fluorescent microscopic images of cells transfected with control (B) or pG2-IRES-EGFP vectors (E). Twenty to 30% of the cells express the construct (green). All cells that fail to exclude Hoechst dye exhibit blue nuclei. (C,F) Red/blue FACS plot of these same cell populations. The pG2-IRES-EGFP–transfected cells exhibit a prominent SP tail (arrow). (D,G) FACS plots of the same cell populations comparing EGFP expression (vertical axis) and Hoechst blue staining (horizontal axis).