GRB2 can be recruited indirectly to KIT through SHP2 (Tauchi et al. 1994). Y279, Y304, Y546 and Y584 (usually referred to as Y542 and Y580 in literature based on the SHP2 short isoform) are the potential sites of SHP2 tyrosyl phosphorylation and that Y546 is the major GRB2 binding site (Feng, et al. 1993, Araki, et al. 2003). This brings Grb2:SOS1 into proximity with the plasma membrane, where it can activate Ras.