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[摘要]：The yeast Saccharomyces cerevisiae responds to amino acid deprivation by increasing translation of the transcription factor Gcn4, which enhances expression of amino acid biosynthetic genes. Accumulation of uncharged tRNAs activates the Gcn2 protein kinase, which phosphorylates the alpha subunit of the eukaryotic initiation factor 2 (eIF2 alpha). The resulting downregulation of eIF2 activity causes reduction of general translation and stimulation of GCN4 translation. S. cerevisiae contains three PDK1 orthologs (encoded by PKH1, PKH2 and PKH3) that have been implicated in nutrient signaling. Using heterologously expressed proteins, we demonstrate physical interaction between Pkh1 and all three subunits of eIF2 as well as Gcn2. We confirm the interaction between Pkh1 and Gcn2 by co-immunoprecipitation in yeast cell extracts and show that Pkh1 can phosphorylate Gcn2 in vitro. However, Pkh1 inactivation did not affect eIF2 alpha-S51 phosphorylation in vivo or GCN4 translation in response to amino acid deprivation. Hence, the physiological importance of the close interactions between Pkh1 and Gcn2 or elF2 could depend on other conditions and/or other targets of the Gcn2/eIF2 system. (C) 2012 Elsevier Inc. All rights reserved. |
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