Differential localization to cytoplasm, nucleus or P-bodies of yeast PKA subunits under different growth conditions

Our aim in this work was to further characterize the complexity and specificity of the three different isoforms (Tpk1, Tpk2 and Tpk3) of the catalytic and regulatory (Bcy1) subunits of PKA in Saccharomyces cerevisiae. We thus analyzed the subcellular localization of the PKA subunits in living cells by using strains carrying GFP (green fluorescent protein) fused to each PKA subunit. During exponential growth on glucose, both Bcy1 and Tpk2 localized in the nucleus, whereas Tpk1 and Tpk3 showed a mixed pattern of nucleo-cytoplasmic localization. During exponential growth on glycerol and during stationary phase, the PKA subunits showed mostly cytoplasmic localization, with the peculiarity that Tpk2 and Tpk3 but not Bcy1, were found associated to P-bodies and EGP bodies. Tpk3 was accumulated into P-bodies during glucose deprivation and hyper osmotic stress. Deletion of Tpk3 altered the kinetics of P-body formation. Analysis of protein expression showed that the relative expression pattern of each Tpk changes from low levels under fermentative metabolism to higher levels during stationary phase. The increase in Tpk levels produced an imbalance with Bcy1 levels. Our data suggest that the signaling specificity through PKA in yeast could be mediated by a particular subcellular localization of each isoform of Tpk.