Phosphorylated SHC1 in the EPOR complex serves as a scaffold to bind GRB2 bound to SOS1 (Damen et al. 1993, Odai et al. 1997). GRB2 may be pre-associated with VAV1 or SOS1, which are guanine nucleotide exchange factors for RAS, or with CBL, an ubiquitin ligase (Odai et al. 1997).