A protein complex of translational regulators of GCN4 mRNA is the guanine nucleotide-exchange factor for translation initiation factor 2 in yeast.
In Saccharomyces cerevisiae, phosphorylation of the alpha subunit of translation initiation factor 2 (eIF-2) by protein kinase GCN2 stimulates translation of GCN4 mRNA. In mammalian cells, phosphorylation of eIF-2 alpha inhibits the activity of eIF-2B, the GDP-GTP exchange factor for eIF-2. We present biochemical evidence that five translational regulators of GCN4 encoded by GCD1, GCD2, GCD6, GCD7, and GCN3 are components of a protein complex that stably interacts with eIF-2 and represents the yeast equivalent of eIF-2B. In vitro, this complex catalyzes guanine nucleotide exchange on eIF-2 and overcomes the inhibitory effect of GDP on formation of eIF-2.GTP.Met-initiator tRNA(Met) ternary complexes. This finding suggests that mutations in GCD-encoded subunits of the complex derepress GCN4 translation because they mimic eIF-2 alpha phosphorylation in decreasing eIF-2B activity. Our results indicate that translational control of GCN4 involves a reduction in eIF-2B function, a mechanism used in mammalian cells to regulate total protein synthesis in response to stress.
Cigan
A M
AM
Section on Molecular Genetics of Lower Eukaryotes, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892.
Bushman
J L
JL
Boal
T R
TR
Hinnebusch
A G
AG
D000595:Amino Acid Sequence; D002846:Chromatography, Affinity; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics; D015852:Eukaryotic Initiation Factor-2 / Q000302:isolation & purification / Q000378:metabolism*; D020717:Eukaryotic Initiation Factor-2B; D005656:Fungal Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D015966:Gene Expression Regulation, Fungal; D020662:Guanine Nucleotide Exchange Factors; D006160:Guanosine Triphosphate / Q000378:metabolism; D007700:Kinetics; D008969:Molecular Sequence Data; D010766:Phosphorylation; D014176:Protein Biosynthesis; D011494:Protein Kinases / Q000096:biosynthesis* / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism*; D012346:RNA, Transfer, Amino Acyl / Q000378:metabolism; D012358:RNA, Transfer, Met; D012097:Repressor Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins
D004268:DNA-Binding Proteins; D015852:Eukaryotic Initiation Factor-2; D020717:Eukaryotic Initiation Factor-2B; D005656:Fungal Proteins; C068999:GCD2 protein, S cerevisiae; C079878:GCD6 protein, S cerevisiae; C079879:GCD7 protein, S cerevisiae; C501390:GCN3 protein, S cerevisiae; D020662:Guanine Nucleotide Exchange Factors; D012333:RNA, Messenger; D012346:RNA, Transfer, Amino Acyl; D012358:RNA, Transfer, Met; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; C024988:tRNA, formylmethionine-; D006160:Guanosine Triphosphate; D011494:Protein Kinases