(E) In vitro phosphorylation assay of CST-1/2 to MIG-2. Bacterially expressed His-tagged MIG-2 or His-tagged MIG-2S139A were incubated with the GST-tagged kinase domain of GST-CST-1/2 (1-318 aa). The kinase may use ATP-γ-S as a phosphodonor to thiophosphorylate its substrate; thus, the phosphorylation reaction was performed with ATP-γ-S, and anti-thiophosphate ester antibody was used to detect substrate phosphorylation (Allen et al, 2005; Allen et al, 2007). The final reaction was probed via immunoblotting with antibodies as indicated. Thio, thiophosphate ester. 