Analysis of DrkA kinase's role in STATa activation.

Dictyostelium is a homologue of metazoan signal transducers and activators of transcription and is important for morphogenesis. duanyu1813a is activated by phosphorylation on Tyr702 when cells are exposed to extracellular cAMP. Although two tyrosine kinase-like (TKL) proteins, Pyk2 and Pyk3, have been definitively identified as kinases, no kinase is known for duanyu1813a activation. Based on homology to the previously identified tyrosine-selective TKLs, we identified DrkA, a member of the TKL family and the Dictyostelium receptor-like kinase (DRK) subfamily, as a candidate duanyu1813a kinase. The drkA gene is almost exclusively expressed in prestalk A (pstA) cells, where duanyu1813a is activated. Transient over-expression of DrkA increased duanyu1813a phosphorylation, although over-expression of the protein causes a severe growth defect and cell death. Furthermore, recombinant DrkA protein is auto-phosphorylated on tyrosine and threonine residues, and an in vitro kinase assay shows that DrkA can phosphorylate duanyu1813a on Tyr702 in a (phosphotyrosine binding) domain-dependent manner. These observations strongly suggest that DrkA is one of the key regulators of duanyu1813a tyrosine phosphorylation and is consistent with it being the kinase that directly activates

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