After ligand-independent dimerization, FGFR1 fusions are trans-autophosphorylated on tyrosine residues (see for instance Popovici, 1998; Ollendorff, 1999; Guasch, 2000). Although the sites of tyrosine phosphorylation have not been mapped in the context of the fusion proteins, at least some of the same residues appear to be phosphorylated as in full length FGFR1. For instance, phospho-specific antibodies have demonstrated that TRIM24 is phosphorylated on Y653 and Y654, the activation loop tyrosines of FGFR1 (Belloni, 2005). Likewise, FGFR1 fusions with ZMYM2, BCR, FGFR1OP and TRIM24 all result in recruitment and phosphorylation of PLCgamma, and where mutational studies have been performed, mutation of the PLCgamma binding site Y766 has been shown to abrogate this signaling (Roumiantsev, 2004, Lelievre, 2008, Chase, 2007). In the case of BCR-FGFR1, the BCR moiety of the fusion protein has also been shown to be phosphorylated on at least one tyrosine residue, Y177, which results in the recruitment of GRB2 (Roumiantsev, 2004).