Themes in Signaling   Ribbon diagram of the PTK domain of FGFR1. The helices are shown in red, the beta strands in green, the nucleotide binding loop in orange, the catalytic loop in blue, the activation loop in purple, the kinase insert in black, and the side chains of Tyr-653 and Tyr 654 in yellow. The Amino and Carboxy termini are denoted by N and C, respectively.