Ectopic expression of ERK1 in NIH 3T3 cells inhibits Ras-mediated colony formation. (a,b) NIH 3T3 cells were transfected as indicated and colony formation was scored after 10 days. Graphs represent quantitations of six independent experiments, expressed as mean ± SEM. Double asterisk indicates a genotype effect that is statistically significant (p < 0.0001), calculated from a post-hoc comparison in one-way ANOVA (Scheffe's test: RasQ61L-ERK1 versus RasQ61L-pMex; RasQ61L-ERK1K72R versus RasQ61L-pMex; RasQ61L-ERK2K52R versus RasQ61L-pMex). (c) A representative plate for each clone from (a,b) is shown.