JAK2 is a member of the Janus kinase (JAKs), which includes JAK1-3 and TYK2. The JAK2 gene is located on the chromosome at 9p24.1. JAKs are non-receptor protein tyrosine kinases that play important roles in regulating hematopoiesis, immune system, and cellular metabolism. Binding of cytokines to the extracellular region of their cognate receptor induces receptor dimerization and promotes trans-phosphorylation (activation) of the associated JAK.