Fig. 4. Activation of ERK5 is required for transformation by oncogenic Src. (A) NIH3T3 cells were transfected with either Y527F Src alone, or with varying amounts of expression plasmids for MEK5AA, wild-type ERK5 or ERK5AEF. After 11-16 days transformed foci were blind scored. (B) NIH3T3 cells were transfected with either of two variants of oncogenic HER2/Neu (neu* or P1*) (see Materials and Methods) alone or with varying amounts of MEK5AA plasmid. Appearance of transformed foci was scored as in A.