Fig. 5. Constitutively active ErbB4 mutants do not increase the growth rate of FR3T3 fibroblasts. FR3T3 cells that express the LXSN vector control, the constitutively active ErbB2* mutant, wild-type ErbB4, or the constitutively active ErbB4 mutants (Q646C, H647C, and A648C) were plated at a density of 2 x 104 cells in 60-mm dishes (700 cells/cm2) and were incubated for 110 days. Cells were counted daily to assess growth rates and saturation densities. The means for three independent experiments; bars, SE.