Multicopy tRNA genes functionally suppress mutations in yeast eIF-2α kinase GCN2: Evidence for separate pathways coupling GCN4 expression to uncharged tRNA

Carlos R. Vazquez De Aldana, Ronald C. Wek, Pedro San Segundo, Alexander G. Truesdell, Alan G. Hinnebusch

Research output: Contribution to journalArticle

35 Scopus citations

Abstract

GCN2 is a protein kinase that stimulates translation of GCN4 mRNA in amino acid-starved cells by phosphorylating the α subunit of translation initiation factor 2 (eIF-2). We isolated multicopy plasmids that overcome the defective derepression of GCN4 and its target genes caused by the leaky mutation gcn2-507. One class of plasmids contained tRNA(His) genes and conferred efficient suppression only when cells were starved for histidine; these plasmids suppressed a gcn2 deletion much less efficiently than they suppressed gcn2-507. This finding indicates that the reduction in GCN4 expression caused by gcn2-507 can be overcome by elevating tRNA(His) expression under conditions in which the excess tRNA cannot be fully aminoacylated. The second class of suppressor plasmids all carried the same gene encoding a mutant form of tRNA(Val) (AAC) with an A-to-G transition at the 3' encoded nucleotide, a mutation shown previously to reduce aminoacylation of tRNA(Val) in vitro. In contrast to the wild-type tRNA(His) genes, the mutant tRNA(Val) gene efficiently suppressed a gcn2 deletion, and this suppression was independent of the phosphorylation site on eIF-2α (Ser- 51). Overexpression of the mutant tRNA(Val) did, however, stimulate GCN4 expression at the translational level. We propose that the multicopy mutant tRNA(Val) construct leads to an accumulation of uncharged tRNA(Val) that derepresses GCN4 translation through a pathway that does not involve GCN2 or eIF-2α phosphorylation. This GCN2-independent pathway was also stimulated to a lesser extent by the multicopy tRNA(His) constructs in histidine-deprived cells. Because the mutant tRNA(Val) exacerbated the slow-growth phenotype associated with eIF-2α hyperphosphorylation by an activated GCN2(c) kinase, we suggest that the GCN2-independent derepression mechanism involves down- regulation of eIF-2 activity.

Original languageEnglish (US)
Pages (from-to)7920-7932
Number of pages13
JournalMolecular and cellular biology
Volume14
Issue number12
DOIs
StatePublished - Dec 1994

ASJC Scopus subject areas

  • Molecular Biology
  • Cell Biology

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