. "FRS2alpha is broadly expressed in adult and fetal tissues. Membrane-bound FRS2alpha interacts with FGFR as a first step in the phosphorylation of this docking protein. The juxtamembrane binding site for FRS2alpha does not contain tyrosine, so binding may be independent of receptor activation and/or constitutive. Activation of the FGFR receptor is required for FRS2alpha phosphorylation and subsequent recruitment of downstream effectors."^^ . . . . .