Recombinant human JAK2 (Janus Kinase 2) encompassing amino acids 536-812, containing the pseudo-kinase domain JH2 with mutations V617F, W659A, W777A, and F794H. This construct contains a C-terminal His-tag (6xHis) followed by an Avi-Tag™. The protein was enzymatically biotinylated using the Avi-Tag™ and affinity purified.