TIF4631 and TIF4632: Two Yeast Genes Encoding the High-Molecular-Weight Subunits of the Cap-Binding Protein Complex (eukaryotic initiation factor 4F) Contain an RNA Recognition Motif-Like Sequence and Carry out an Essential Function

Abstract

The 5' ends of eukaryotic mRNAs are blocked by a cap structure, m7GpppX (where X is any nucleotide). The interaction of the cap structure with a cap-binding protein complex is required for efficient ribosome binding to the mRNA. In Saccharomyces cerevisiae, the cap-binding protein complex is a heterodimer composed of two subunits with molecular masses of 24 (eIF-4E, CDC33) and 150 (p150) kDa. p150 is presumed to be the yeast homolog of the p220 component of mammalian eIF-4F. In this report, we describe the isolation of yeast gene TIF4631, which encodes p150, and a closely related gene, TIF4632. TIF4631 and TIF4632 are 53% identical overall and 80% identical over a 320-amino-acid stretch in their carboxy-terminal halves. Both proteins contain sequences resembling the RNA recognition motif and auxiliary domains that are characteristic of a large family of RNA-binding proteins. tif4631-disrupted strains exhibited a slow-growth, cold-sensitive phenotype, while disruption of TIF4632 failed to show any phenotype under the conditions assayed. Double gene disruption engendered lethality, suggesting that the two genes are functionally homologous and demonstrating that at least one of them is essential for viability. These data are consistent with a critical role for the high-molecular-weight subunit of putative yeast eIF-4F in translation. Sequence comparison of TIF4631, TIF4632, and the human eIF-4F p220 subunit revealed significant stretches of homology. We have thus cloned two yeast homologs of mammalian p220.

A newly identified N-terminal amino acid sequence of human eIF4G binds poly(A)-binding protein and functions in poly(A)-dependent translation

“…eIF4G is required for both cap‐dependent and cap‐independent translation (Belsham and Sonenberg, 1996; Morley et al ., 1997; Sachs et al ., 1997). One mechanism by which eIF4G functions in both cap‐dependent and cap‐independent ribosome binding is to bind the mRNA, presumably through the RRM‐like sequence in the middle domain of the protein (Goyer et al ., 1993). The RNA‐binding activity of the middle domain of eIF4G is sufficient to promote cap‐independent translation, as this domain was shown to interact tightly with a specific sequence in the internal ribosome entry site of the encephalomyocarditis virus RNA (Pestova et al ., 1996).…”

The eukaryotic mRNA decapping protein Dcp1 interacts physically and functionally with the eIF4F translation initiation complex

“…The eukaryotic initiation factor complex eIF4F comprises the cap‐binding protein eIF4E (∼25 kDa), a much larger factor called eIF4G and the DEAD box (helicase) protein eIF4A (Merrick and Hershey, 1996; Gingras et al ., 1999). Saccharomyces cerevisae has two versions of eIF4G (Goyer et al ., 1993), eIF4G1 (107 kDa) and eIF4G2 (104 kDa). The association between eIF4G and eIF4A appears to be much less stable in yeast, and the latter factor binds in greatly substoichiometric amounts to eIF4G (Dominguez et al ., 1999; Neff and Sachs, 1999).…”

Specific mechanisms of translation initiation in higher eukaryotes: the eIF4G2 story

“…Since the discovery of the eIF4F complex, the initiation mechanism involving eIF4G1 has been regarded as the principal one. Although eIF4G1 is indeed vital for the development of organisms (Contreras et al 2008;Goyer et al 1993), its partial depletion in yeast or mammalian cells, contrary to expectations, does not have a critical effect on cell growth and viability under normal conditions (Badura et al 2012;Ramírez-Valle et al 2008;Park et al 2011;Bryant et al 2018).…”