FIG. 3.

Transformation assays of 208F cells with the Env chimeras. 208F cells were transfected with chimeric and wild-type Env expression plasmids as described in the text. Transfected cells were examined by light microscopy for morphological alterations at 2 weeks postinfection. Cell transformation, represented by the formation of foci of refractive cells, was achieved with the expression plasmids for the JSRV Env (B) and MMuLVprr-JSE (E). Some morphological changes were observed with MMuLVrbd-JSE (F) and MMTVprr-JSE (H). No signs of cell transformation were observed in mock-transfected cells (A) or in cells transfected with pCEE+ (C) (expressing the MMuLV Env), pENV (Q61) (D) (expressing the MMTV Env), MMTVrbd-JSE (G), or MMuLV-JSct1 (J). (K) The 208F-23 cell line, derived from the isolation and expansion of MMuLVprr-JSE-transformed cells. 208F-23 cells have lost the contact inhibition typical of 208F cells.