FIG. 4.

MMTV Sag expression in B cells is independent of the sag gene intragenic enhancer. Reporter plasmids pM^sag17-luc(E_proB^+/+) (open circles) and pM^sag17-luc(E_proB^+/−) (open squares), with their respective truncation mutants Δ5055, Δ5803, Δ7478, and Δ8532, and luciferase control plasmid CMV-luc (solid squares) were transfected into either Ba/F3 pro-B cells (top) or B-cell hybridoma LBB.11 (bottom). The mock transfection is represented by solid circles. We used 2 pmol of each test plasmid, except for CMV-luc, for which we used 0.5 pmol of plasmid. Cells were harvested after 24 h, and luciferase activity was determined. Results are expressed as relative luciferase units (RLU) per microgram of protein and represent the arithmetic mean ± SD of at least three separate experiments with two different DNA preparations. The viral constructs with nucleotide positions are depicted below the graphs. The approximate positions of coding regions (gag, pol, and env), promoters (P), and reporter gene luciferase (luc) are shown. The specific constructs transfected are identified above the graphs.