GCN1, a Translational Activator of GCN4 in Saccharomyces cerevisiae, is Required for Phosphorylation of Eukaryotic Translation Initiation Factor 2 by Protein Kinase GCN2

Phosphorylation of eIF-2 alpha by GCN2 is dependent on the previously uncharacterized gene GCN1.

• GCN1 is necessary for the increased translation of GCN4 in amino acid-starved yeast cells.
• Inactivation of GCN1 does not alter eIF-2 alpha phosphorylation when mammalian kinases are used, suggesting GCN1 does not participate in dephosphorylation.
• Cell extracts from gcn1 delta strains retain normal levels of GCN2 kinase activity, indicating GCN1 is not required for the kinase's activity itself.
• GCN1 appears essential for the in vivo activation of GCN2 in response to uncharged tRNA, a starvation signal.
• The GCN1 protein is 297 kDa and contains a region similar to translation elongation factor 3, suggesting a potential role in interacting with ribosomes or tRNA.

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