Schematic representation of FGFR1, FOP, and both FOP-FGFR1 and FGFR1-FOP fusion proteins. FGFR1 domains are indicated as follows: IgI, IgII, and IgIII, the three Ig-like domains; TM, the transmembrane domain; and TK1 and TK2, the tyrosine kinase 1 and 2 subdomains interrupted by a kinase insert (KI). Waved lines in the N- and C-terminal parts of FOP represent the leucine-rich repeats. FGFR1-FOP retains the extracellular and transmembrane domains of FGFR1, whereas FOP-FGFR1 fusion protein contains the FGFR1 catalytic domain. Double arrows indicate the t(6;8) breakpoint. Nucleotide and amino acid breakpoint sequences are indicated for both resultant chimeric products.