Western Blot analysis of extracts from COS cells, untransfected (lane 1) or transfected with either wild-type (lanes 2 and 3) or Ala916 mutant (lanes 4 and 5) Ras-GRF1, using Phospho-Ras-GRF1 (Ser916) Antibody (upper) or Ras-GRF1 R1198-16 (lower). Transfected COS cells were untreated or treated forskolin as indicated.(Triple HA-tagged Ras-GRF1 expressing plasmids provided by Dr. R. Mattingly, Dept. of Pharmacology, Wayne State University, Michigan.)