Figure 5.

Effect of dominant-negative Ras on the activation of the MAP kinase ERK2 by v-Src. (A) CEF were infected as in Fig. 2A, and the activity of endogenous ERK2 was determined as described. (B) CEF were infected as in Fig. 2A, except that a temperature-sensitive mutant of v-Src (tsUP1) was used. Cells were maintained at the nonpermissive temperature (41°C) during the entire incubation period (Temp. Shift, −) or were shifted to the permissive temperature (36°C) 30 min prior to lysis (Temp. Shift, +). The activity of endogenous ERK2 was then determined as described. (C) Rat-2-derived cell lines carrying the empty metal-inducible expression vector (pM2N-1), metal-inducible N17Ras (N17Ras-2), or clones of these cells that also express v-Src (pM2NSrc and N17RasSrc) were assayed for the activity of endogenous ERK2 as described. Numbers below the autoradiograms refer to the radioactivity incorporated into the substrate (myelin basic protein, MBP) as determined by PhosphorImager analysis, and are expressed as percentages relative to the vector control lanes.