A proposed structure of JAK2. The ribbon diagrams of the JH1 (predominant color blue) and JH2 (predominant color green) domains of JAK2 are shown, modeled on the structure of the dimeric fibroblast growth factor receptor structure. The activation loop of JH1 is shown in 2 possible conformations, active (red) and inactive (blue). The kinase site is shown in orange and the adenosine triphosphate (ATP) binding site in yellow. The site of interaction of JH2 and the activation domain of JH1 is shown encircled, along with the location of Val617. Adapted from Lindauer et al²⁶  and reproduced with permission of Oxford University Press.