The protein kinase YakA regulates G-protein-linked signaling responses during growth and development of Dictyostelium

A genetic screen for Dictyostelium mutants that phenotypically resemble cel ls lacking the G-protein beta -subunit yielded the protein kinase YakA. Lik e g beta -null cells, yakA-null cells fail to enter development and display slow growth on bacterial lawns. We created a temperature-sensitive yakA mu tant and showed that YakA activity is required not only at the onset but al so during development. The yakA-null cells have strong defects in folic aci d-induced responses, such as actin polymerization and cGMP accumulation, in dicating that they play a role in G-protein-mediated signaling responses. W e propose that YakA acts downstream of G-proteins, because cAMP receptors s till couple to G-proteins in the yakA mutant. In addition, the previously o bserved growth arrest induced by overexpression of YakA also occurs in g be ta mutants. We localized YakA-GFP to the cytosol suggesting that YakA may b e a functional homolog of its mammalian counterparts Dyrk2 and Dyrk3, a sub class of dual-specificity Yak-related kinases (Dyrk) with unknown function.