FIG. 2.

LMP1^TRADD is not sufficient for MEF immortalization. (A) MEF were infected with retroviruses carrying genes for LNSX, LMP1, or LMP1^TRADD at passage 3. They were subsequently split 1:2 whenever they reached confluence in the absence of any drug selection. MEF-LNSX cells had a limited life span of 10 passages (10 population doublings) and did not reach confluence afterwards. MEF-LMP1^TRADD cells had an extended passage number of 19 in about 3 months but ceased proliferating afterwards. (B) Transient induction of S-phase-specific cyclin A by LMP1^TRADD. Cell lysates were obtained from the infected MEF at the indicated passages and examined for the expression of cyclin A by Western blotting. A blot against β-actin was used to control loading.