Tyrosine-phosphorylated SHC1 recruits the SH2 domain of the adaptor protein GRB2, which is complexed with SOS1, an exchange factor for p21 Ras and Rac. GRB2 binds SOS1 through its SH3 domain. This domain can associate with other intracellular targets, including GAB1. ERK and Rsk mediated phosphorylation results in dissociation of the SOS1:GRB2 complex. This may explain why ERK activation through SHC and GRB2:SOS1 is transient. Inactive p21 Ras-GDP is found anchored to the plasma membrane by a farnesyl residue. As SHC is phosphorylated by the the stimulated receptor near to the plasma membrane, the GRB2:SOS1:SHC interaction brings SOS1 into close proximity to p21 Ras.