B. A. Witthuhn

B. A. Witthuhn is the first author of a 1993 study connecting the erythropoietin receptor to the protein kinase JAK2. The biological puzzle was how erythropoietin could stimulate tyrosine phosphorylation through a receptor that lacks its own kinase protein domain. The experiments showed that JAK2 physically associates with an intracellular region of the erythropoietin receptor.^[ref]

Adding erythropoietin induced JAK2 tyrosine phosphorylation and increased its autophosphorylation activity. Experiments with altered erythropoietin receptors connected these changes with the ability to stimulate cell multiplication. This supplied a concrete mechanism for signal transduction: a receptor without an intrinsic kinase protein domain can recruit a separate protein kinase. The combination of physical association, regulated activity and altered-receptor tests is more informative than any one measurement alone.^[ref]