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Structural highlights

Function

[EIF3B_YEAST] Component of the eukaryotic translation initiation factor 3 (eIF-3) complex, which is involved in protein synthesis and, together with other initiation factors, stimulates binding of mRNA and methionyl-tRNAi to the 40S ribosome.^[1] [RS21_KLULA] Required for the processing of the 20S rRNA-precursor to mature 18S rRNA in a late step of the maturation of 40S ribosomal subunits. Has a physiological role leading to 18S rRNA stability (By similarity). [IF2G_YEAST] eIF-2 functions in the early steps of protein synthesis by forming a ternary complex with GTP and initiator tRNA. This complex binds to a 40S ribosomal subunit, followed by mRNA binding to form a 43S preinitiation complex. Junction of the 60S ribosomal subunit to form the 80S initiation complex is preceded by hydrolysis of the GTP bound to eIF-2 and release of an eIF-2-GDP binary complex. In order for eIF-2 to recycle and catalyze another round of initiation, the GDP bound to eIF-2 must exchange with GTP by way of a reaction catalyzed by eIF-2B. [RS27A_KLULA] Ubiquitin exists either covalently attached to another protein, or free (unanchored). When covalently bound, it is conjugated to target proteins via an isopeptide bond either as a monomer (monoubiquitin), a polymer linked via different Lys residues of the ubiquitin (polyubiquitin chains) or a linear polymer linked via the initiator Met of the ubiquitin (linear polyubiquitin chains). Polyubiquitin chains, when attached to a target protein, have different functions depending on the Lys residue of the ubiquitin that is linked: Lys-6-linked may be involved in DNA repair; Lys-11-linked is involved in ERAD (endoplasmic reticulum-associated degradation) and in cell-cycle regulation; Lys-29-linked is involved in lysosomal degradation; Lys-33-linked is involved in kinase modification; Lys-48-linked is involved in protein degradation via the proteasome; Lys-63-linked is involved in endocytosis, and DNA-damage responses. Linear polymer chains formed via attachment by the initiator Met lead to cell signaling. Ubiquitin is usually conjugated to Lys residues of target proteins, however, in rare cases, conjugation to Cys or Ser residues has been observed. When polyubiquitin is free (unanchored-polyubiquitin), it also has distinct roles, such as in activation of protein kinases, and in signaling (By similarity). Ribosomal protein S27a is a component of the 40S subunit of the ribosome. [IF5_YEAST] Catalyzes the hydrolysis of GTP bound to the 40S ribosomal initiation complex (40S.mRNA.Met-tRNA[F].eIF-2.GTP) with the subsequent joining of a 60S ribosomal subunit resulting in the release of eIF-2 and the guanine nucleotide. The subsequent joining of a 60S ribosomal subunit results in the formation of a functional 80S initiation complex (80S.mRNA.Met-tRNA[F]). eIF-5 is essential for cell viability.^[2] [EIF3G_YEAS7] Component of the eukaryotic translation initiation factor 3 (eIF-3) complex, which is involved in protein synthesis and, together with other initiation factors, stimulates binding of mRNA and methionyl-tRNAi to the 40S ribosome. This subunit can bind 18S rRNA.[HAMAP-Rule:MF_03006] [IF2A_YEAST] eIF-2 functions in the early steps of protein synthesis by forming a ternary complex with GTP and initiator tRNA. This complex binds to a 40S ribosomal subunit, followed by mRNA binding to form a 43S preinitiation complex. Junction of the 60S ribosomal subunit to form the 80S initiation complex is preceded by hydrolysis of the GTP bound to eIF-2 and release of an eIF-2-GDP binary complex. In order for eIF-2 to recycle and catalyze another round of initiation, the GDP bound to eIF-2 must exchange with GTP by way of a reaction catalyzed by eIF-2B. [IF2B_YEAST] eIF-2 functions in the early steps of protein synthesis by forming a ternary complex with GTP and initiator tRNA. This complex binds to a 40S ribosomal subunit, followed by mRNA binding to form a 43S preinitiation complex. Junction of the 60S ribosomal subunit to form the 80S initiation complex is preceded by hydrolysis of the GTP bound to eIF-2 and release of an eIF-2-GDP binary complex. In order for eIF-2 to recycle and catalyze another round of initiation, the GDP bound to eIF-2 must exchange with GTP by way of a reaction catalyzed by eIF-2B. [EIF3I_YEAS7] Component of the eukaryotic translation initiation factor 3 (eIF-3) complex, which is involved in protein synthesis and, together with other initiation factors, stimulates binding of mRNA and methionyl-tRNAi to the 40S ribosome (By similarity). [IF1A_YEAST] Seems to be required for maximal rate of protein biosynthesis. Enhances ribosome dissociation into subunits and stabilizes the binding of the initiator Met-tRNA(I) to 40 S ribosomal subunits. [RSSA_KLULA] Required for the assembly and/or stability of the 40S ribosomal subunit. Required for the processing of the 20S rRNA-precursor to mature 18S rRNA in a late step of the maturation of 40S ribosomal subunits. [EIF3A_YEAST] Component of the eukaryotic translation initiation factor 3 (eIF-3) complex, which is involved in protein synthesis and, together with other initiation factors, stimulates binding of mRNA and methionyl-tRNAi to the 40S ribosome.^{[3] [4] [5] [6]}

See Also

• Ribosome 3D structures

References

1. ↑ Phan L, Schoenfeld LW, Valasek L, Nielsen KH, Hinnebusch AG. A subcomplex of three eIF3 subunits binds eIF1 and eIF5 and stimulates ribosome binding of mRNA and tRNA(i)Met. EMBO J. 2001 Jun 1;20(11):2954-65. PMID:11387228 doi:http://dx.doi.org/10.1093/emboj/20.11.2954
2. ↑ Valasek L, Mathew AA, Shin BS, Nielsen KH, Szamecz B, Hinnebusch AG. The yeast eIF3 subunits TIF32/a, NIP1/c, and eIF5 make critical connections with the 40S ribosome in vivo. Genes Dev. 2003 Mar 15;17(6):786-99. PMID:12651896 doi:http://dx.doi.org/10.1101/gad.1065403
3. ↑ Valasek L, Trachsel H, Hasek J, Ruis H. Rpg1, the Saccharomyces cerevisiae homologue of the largest subunit of mammalian translation initiation factor 3, is required for translational activity. J Biol Chem. 1998 Aug 14;273(33):21253-60. PMID:9694884
4. ↑ Phan L, Schoenfeld LW, Valasek L, Nielsen KH, Hinnebusch AG. A subcomplex of three eIF3 subunits binds eIF1 and eIF5 and stimulates ribosome binding of mRNA and tRNA(i)Met. EMBO J. 2001 Jun 1;20(11):2954-65. PMID:11387228 doi:http://dx.doi.org/10.1093/emboj/20.11.2954
5. ↑ Valasek L, Mathew AA, Shin BS, Nielsen KH, Szamecz B, Hinnebusch AG. The yeast eIF3 subunits TIF32/a, NIP1/c, and eIF5 make critical connections with the 40S ribosome in vivo. Genes Dev. 2003 Mar 15;17(6):786-99. PMID:12651896 doi:http://dx.doi.org/10.1101/gad.1065403
6. ↑ Szamecz B, Rutkai E, Cuchalova L, Munzarova V, Herrmannova A, Nielsen KH, Burela L, Hinnebusch AG, Valasek L. eIF3a cooperates with sequences 5' of uORF1 to promote resumption of scanning by post-termination ribosomes for reinitiation on GCN4 mRNA. Genes Dev. 2008 Sep 1;22(17):2414-25. doi: 10.1101/gad.480508. PMID:18765792 doi:http://dx.doi.org/10.1101/gad.480508
7. ↑ Llacer JL, Hussain T, Saini AK, Nanda JS, Kaur S, Gordiyenko Y, Kumar R, Hinnebusch AG, Lorsch JR, Ramakrishnan V. Translational initiation factor eIF5 replaces eIF1 on the 40S ribosomal subunit to promote start-codon recognition. Elife. 2018 Nov 26;7. pii: 39273. doi: 10.7554/eLife.39273. PMID:30475211 doi:http://dx.doi.org/10.7554/eLife.39273