As an important member of AGC (cAMP- and cGMP-dependent protein kinases and protein kinase C) family kinases，Saccharomyces cerevisiae protein kinase Sch9 (orthologue of mammalian protein kinase S6K1) participates in lots of cellular biological regulation processes such as lifespan,?autophagy, stress response and cellular respiration.The phosphorylation levels of two main phosphorylation sites on Sch9,namely PDK1 site and PDK2 site,are regulated by protein kinases of their upstream and the alterant phosphorylation also changes Sch9 activity.In this way,Sch9 seems like a signal hinge to transfer biological signals.Using two mutants of point mutation of PDK1 and PDK2 sites,growth assay,chronological lifespan detection and western blotting were done.We demonstrated that phosphorylation at the PDK1 site is indispensable for Sch9 activity.In addition,dephosphorylation at PDK1 site can induce prominent phosphorylation at C terminal.On?the?contrary,phosphorylation of the PDK1 site depresses phosphorylation at C terminal.Thus,phosphorylation conditions of PDK1 and PDK2 site on Sch9 are not only regulated by theirself-upstream,but also influenced by a negative control mechanism existing in their interaction.
