tokens: A reciprocal binding assay using IM - 9 cells as a source of SHP - 1 and SHP - 2 revealed specific association of SHP - 2 ( but not SHP - 1 ) with a glutathione S - transferase fusion incorporating GHR cytoplasmic domain residues 485 - 620 , but only if the fusion was first rendered tyrosine - phosphorylated .