sentences:  FGFR1-4 are cell surface membrane receptors that possess tyrosine kinase activity.A full-length representative of these four receptors consists of an extracellular region composed of three immunoglobulin-like domains which bind their proper ligands, the fibroblast growth factors (FGFs), a single hydrophobic stretch which passes through the cell's surface membrane, and a cytoplasmic tyrosine kinase domain.When bonded to FGFs, these receptors form dimers with any one of the four other FGFRs and then cross-phosphorylate key tyrosine residues on their dimer partners.