Mammalian eukaryotic initiation factor 2 alpha kinases functionally substitute for GCN2 protein kinase in the GCN4 translational control mechanism of yeast.
Phosphorylation of the alpha subunit of eukaryotic initiation factor 2 (eIF-2 alpha) in Saccharomyces cerevisiae by the GCN2 protein kinase stimulates the translation of GCN4 mRNA. The protein kinases heme-regulated inhibitor of translation (HRI) and double-stranded RNA-dependent eIF-2 alpha protein kinase (dsRNA-PK) inhibit initiation of translation in mammalian cells by phosphorylating Ser-51 of eIF-2 alpha. We show that HRI and dsRNA-PK phosphorylate yeast eIF-2 alpha in vitro and in vivo and functionally substitute for GCN2 protein to stimulate GCN4 translation in yeast. In addition, high-level expression of either mammalian kinase in yeast decreases the growth rate, a finding analogous to the inhibition of total protein synthesis by these kinases in mammalian cells. Phosphorylation of eIF-2 alpha inhibits initiation in mammalian cells by sequestering eIF-2B, the factor required for exchange of GTP for GDP on eIF-2. Mutations in the GCN3 gene, encoding a subunit of the yeast eIF-2B complex, eliminate the effects of HRI and dsRNA-PK on global and GCN4-specific translation in yeast. These results provide further in vivo evidence that phosphorylation of eIF-2 alpha inhibits translation by impairing eIF-2B function and identify GCN3 as a regulatory subunit of eIF-2B. These results also suggest that GCN4 translational control will be a good model system to study how mammalian eIF-2 alpha kinases are modulated by environmental signals and viral regulatory factors.
Dever
T E
TE
Section on Molecular Genetics of Lower Eukaryotes, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892.
Chen
J J
JJ
Barber
G N
GN
Cigan
A M
AM
Feng
L
L
Donahue
T F
TF
London
I M
IM
Katze
M G
MG
Hinnebusch
A G
AG
D000818:Animals; D004268:DNA-Binding Proteins; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism*; D020717:Eukaryotic Initiation Factor-2B; D005656:Fungal Proteins / Q000378:metabolism*; D015966:Gene Expression Regulation, Fungal; D008322:Mammals; D010766:Phosphorylation; D014176:Protein Biosynthesis; D011494:Protein Kinases / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins; D013045:Species Specificity; D019892:eIF-2 Kinase
D004268:DNA-Binding Proteins; D015852:Eukaryotic Initiation Factor-2; D020717:Eukaryotic Initiation Factor-2B; D005656:Fungal Proteins; C501390:GCN3 protein, S cerevisiae; D012333:RNA, Messenger; D029701:Saccharomyces cerevisiae Proteins; D011494:Protein Kinases; D019892:eIF-2 Kinase