Truncated protein phosphatase GLC7 restores translational activation of GCN4 expression in yeast mutants defective for the eIF-2 alpha kinase GCN2.

Abstract

GCN2 is a protein kinase in Saccharomyces cerevisiae that is required for increased expression of the transcriptional activator GCN4 in amino acid-starved cells. GCN2 stimulates GCN4 synthesis at the translational level by phosphorylating the alpha subunit of eukaryotic translation initiation factor 2 (eIF-2). We identified a truncated form of the GLC7 gene, encoding the catalytic subunit of a type 1 protein phosphatase, by its ability to restore derepression of GCN4 expression in a strain containing the partially defective gcn2-507 allele. Genetic analysis suggests that the truncated GLC7 allele has a dominant negative phenotype, reducing the level of native type 1 protein phosphatase activity in the cell. The truncated form of GLC7 does not suppress the regulatory defect associated with a gcn2 deletion or a mutation in the phosphorylation site of eIF-2 alpha (Ser-51). In addition, the presence of multiple copies of wild-type GLC7 impairs the derepression of GCN4 that occurs in response to amino acid starvation or dominant-activating mutations in GCN2. These findings suggest that the phosphatase activity of GLC7 acts in opposition to the kinase activity of GCN2 in modulating the level of eIF-2 alpha phosphorylation and the translational efficiency of GCN4 mRNA. This conclusion is supported by biochemical studies showing that the truncated GLC7 allele increases the level of eIF-2 alpha phosphorylation in the gcn2-507 mutant to a level approaching that seen in wild-type cells under starvation conditions. The truncated GLC7 allele also leads to reduced glycogen accumulation, indicating that this protein phosphatase is involved in regulating diverse metabolic pathways in yeast cells.

• Authors: R C Wek, J F Cannon, T E Dever, A G Hinnebusch
• Journal: Molecular and cellular biology (Mol Cell Biol) Vol. 12 Issue 12 Pg. 5700-10 (Dec 1992) ISSN: 0270-7306 [Print] United States
• PMID: 1333044 (Publication Type: Journal Article)

Chemical References

• Saccharomyces cerevisiae Proteins
• Histidine
• Protein Kinases
• GCN2 protein, S cerevisiae
• Protein Serine-Threonine Kinases
• Phosphoprotein Phosphatases

Topics

• Alleles
• Gene Expression Regulation, Fungal
• Genetic Complementation Test
• Histidine (biosynthesis, genetics)
• Phosphoprotein Phosphatases (metabolism)
• Phosphorylation
• Plasmids
• Protein Biosynthesis
• Protein Kinases (genetics, metabolism)
• Protein Serine-Threonine Kinases
• Restriction Mapping
• Saccharomyces cerevisiae (enzymology, genetics)
• Saccharomyces cerevisiae Proteins
• Suppression, Genetic