In Vitro Kinase Assay with Recombinant SnRK2s: An Example for Assaying Stress-Responsive Kinases in Plants

Protein phosphorylation is one of the most important posttranslational modifications in cell signaling pathways. Kinases and phosphatases play essential roles in transferring information between sensors and effectors under stress conditions. Several methods have been developed to analyze the phosphorylation mechanisms. Each method has advantages and disadvantages. In vitro kinase assay using recombinant proteins is a method to analyze kinase activities under simplified conditions. It is a good strategy to understand each mechanism one by one, although it is not always suitable to estimate the feature of complex machinery in vivo. In this chapter, the purification of recombinant proteins produced in Escherichia coli followed by assaying a kinase activity using radioactivity is described.