FIG. 5.

The ENTV and JSRV env genes induce transformed foci in cultured mouse cells. A morphologically flat subline of NIH 3T3 mouse cells (originally from Doug Lowy) was seeded at 5 × 10⁵ cells per 6-cm-diameter dish. One day later, the cells were transfected with 10 μg each of the plasmids pSX2.Eenv (ENTV env), pSX2.Jenv (JSRV env), pSX2 (10A1 env) or pFBJ/R (viral fos oncogene) (23) plus 1 μg of pLAPSN (to measure transfection efficiency) by using the CaPO₄ coprecipitation method. One day after transfection, the cells were trypsinized and divided in a 1:5 ratio into new dishes. Four days after transfection, the medium was changed to medium containing 5% fetal bovine serum, and the cells were refed with this medium every 3 days thereafter. Eleven days after transfection, the cells were fixed and stained for AP. Representative foci are shown; no foci were observed in the 10A1 env dish. Two AP⁺ cells are visible at the lower right in the 10A1 env panel.