Following association with KIT, Tauchi et al. had observed phosphorylation of SHP2 (Tauchi et al. 1994). Tyrosine residues Y546 and Y584 (usually referred to as Y542 and Y580 in literature based on the short isoform) are the major sites of SHP2 tyrosyl phosphorylation. Src family kinases (SFKs) are candidates for this phosphorylation (Araki et al. 2003). The phosphorylated tyrosine residues on SHP2 can recruit the adapter protein GRB2 (Tauchi et al. 1994), but it is unclear whether GRB2 binding to SHP2 is important for KIT mediated SHP2 signaling or whether the effect of SHP2 on the RAS/ERK pathway goes through its catalytic activity.