FIG. 7.

The myristoylated Sos N terminus inhibits EGF-induced MAPK activity in NIH 3T3 cells; importance of Dbl and PH domains. NIH 3T3 cells transiently cotransfected with HA-MAPK and empty vector, MyrSos1-NT, or MyrSos1-NT(Dbl∼PH∗/#) were serum starved and then treated with EGF (50 ng/ml) for 5 min at 37°C. The immunocomplexes were formed and analyzed for in vitro MAPK assays as described in Materials and Methods and in the legend to Fig. 4. Compared with the vector alone (100%), the amounts of MBP were 48% for MyrSos1-NT and 71% for MyrSos1-NT(Dbl∼PH∗/#). Expression of the exogenous HA-MAPK in these transiently transfected cells was confirmed by anti-HA blotting. Similar results were obtained in two other experiments.