Eukaryotic eIF-5A was initially thought to function as a translation initiation factor, based on its ability to stimulate methionyl-puromycin synthesis. However, subsequent work revealed a role for eIF5A in translation elongation [, ]. Depletion or inactivation of eIF-5A in the yeast Saccharomyces cerevisiae (Baker's yeast) resulted in the accumulation of polysomes and an increase in ribosomal transit times. Addition of recombinant eIF-5A from yeast, but not a derivative lacking hypusine, enhanced the rate of tripeptide synthesis in vitro. Moreover, inactivation of eIF-5A mimicked the effects of the eEF2 inhibitor sordarin, indicating that eIF-5A might function together with eEF2 to promote ribosomal translocation. Finally, it was shown that eIF5A is specifically required to promote peptide-bond formation between consecutive proline residues. It has been proposed to stimulate the peptidyl-transferase activity of the ribosome and facilitate the reactivity of poor substrates like proline [].eIF-5A is a cofactor for the Rev and Rex transactivator proteins of human immunodeficiency virus-1 and T-cell leukaemia virus I, respectively [, , ]. IF-5A is the sole protein in eukaryotes and archaea to contain the unusual amino acid hypusine (Ne-(4-amino-2-hydroxybutyl)lysine) that is an absolute functional requirement. The first step in the post-translational modification of lysine to hypusine is catalyzed by the enzyme deoxyhypusine synthase, the structure of which has been reported []. The archaeal IF-5A proteins have not been studied as comprehensively as their eukaryotic homologues, though the crystal structure of the Pyrobaculum aerophilum protein has been determined. Unmodified P. aerophilum IF-5A is found to be a beta structure with two domains and three separate hydrophobic cores. The lysine (Lys42) that is post-translationally modified by deoxyhypusine synthase is found at one end of the IF-5A molecule in a turn between beta strands beta4 and beta5; this lysine residue is freely solvent accessible. The C-terminal domain is found to be homologous to the cold-shock protein CspA of E. coli, which has a well characterised RNA-binding fold, suggesting that IF-5A is involved in RNA binding [].This entry represents the archaeal IF-5A proteins.
Eukaryotic eIF-5A was initially thought to function as a translation initiation factor, based on its ability to stimulate methionyl-puromycin synthesis. However, subsequent work revealed a role for eIF5A in translation elongation [, ]. Depletion or inactivation of eIF-5A in the yeast Saccharomyces cerevisiae (Baker's yeast) resulted in the accumulation of polysomes and an increase in ribosomal transit times. Addition of recombinant eIF-5A from yeast, but not a derivative lacking hypusine, enhanced the rate of tripeptide synthesis in vitro. Moreover, inactivation of eIF-5A mimicked the effects of the eEF2 inhibitor sordarin, indicating that eIF-5A might function together with eEF2 to promote ribosomal translocation. Finally, it was shown that eIF5A is specifically required to promote peptide-bond formation between consecutive proline residues. It has been proposed to stimulate the peptidyl-transferase activity of the ribosome and facilitate the reactivity of poor substrates like proline [].eIF-5A is a cofactor for the Rev and Rex transactivator proteins of human immunodeficiency virus-1 and T-cell leukaemia virus I, respectively [, , ]. IF-5A is the sole protein in eukaryotes and archaea to contain the unusual amino acid hypusine (Ne-(4-amino-2-hydroxybutyl)lysine) that is an absolute functional requirement. The first step in the post-translational modification of lysine to hypusine is catalyzed by the enzyme deoxyhypusine synthase, the structure of which has been reported []. The archaeal IF-5A proteins have not been studied as comprehensively as their eukaryotic homologues, though the crystal structure of the Pyrobaculum aerophilum protein has been determined. Unmodified P. aerophilum IF-5A is found to be a beta structure with two domains and three separate hydrophobic cores. The lysine (Lys42) that is post-translationally modified by deoxyhypusine synthase is found at one end of the IF-5A molecule in a turn between beta strands beta4 and beta5; this lysine residue is freely solvent accessible.The C-terminal domain is found to be homologous to the cold-shock protein CspA of E. coli, which has a well characterised RNA-binding fold, suggesting that IF-5A is involved in RNA binding [].This family also includes the Woronin body major protein Hex1, whose sequence and structure are similar to eukaryotic initiation factor 5A (eIF5A), suggesting they share a common ancestor during evolution []. Woronin bodies are important for stress resistance and virulence [].
Elongation factor P (EF-P) stimulates the peptidyltransferase activity in the prokaryotic 70S ribosome. EF-P enhances the synthesis of certain dipeptides with N-formylmethionyl-tRNA and puromycine in vitro. EF-P binds to both the 30S and 50S ribosomal subunits. EF-P binds near the streptomycine binding site of the 16S rRNA in the 30S subunit. EF-P interacts with domains 2 and 5 of the 23S rRNA. The L16 ribosomal protein of the 50S or its N-terminal fragment are required for EF-P mediated peptide bond synthesis, whereas L11, L15, and L7/L12 are not required in this reaction, suggesting that EF-P may function at a different ribosomal site than most other translation factors. EF-P is essential for cell viability and is required for protein synthesis [, , , ]. EF-P is mainly present in bacteria. The EF-P homologs in archaea and eukaryotes are the initiation factors aIF5A and eIF5A, respectively. EF-P has 3 domains (domains I, II, and III). Domains II and III are S1-like domains. This entry includes domain III (the second S1 domain of EF_P). Domains II and III of have structural homology to the eIF5A domain C, suggesting that domains II and III evolved by duplication. These domains adopt an OB-fold, with five β-strands forming a β-barrel in a Greek-key topology [].
Elongation factor P (EF-P) is a prokaryotic protein translation factor required for efficient peptide bond synthesis on 70S ribosomes from fMet-tRNAfMet [, ]. EF-P enhances the synthesis of certain dipeptides with N-formylmethionyl-tRNA and puromycine in vitro. EF-P binds to both the 30S and 50S ribosomal subunits. EF-P binds near the streptomycine binding site of the 16S rRNA in the 30S subunit. EF-P interacts with domains 2 and 5 of the 23S rRNA. The L16 ribosomal protein of the 50S or its N-terminal fragment are required for EF-P mediated peptide bond synthesis, whereas L11, L15, and L7/L12 are not required in this reaction, suggesting that EF-P may function at a different ribosomal site than most other translation factors. EF-P is essential for cell viability and is required for protein synthesis. EF-P is mainly present in bacteria. The EF-P homologs in archaea and eukaryotes are the initiation factors aIF5A and eIF5A, respectively. EF-P has 3 domains (domains I, II, and III). Domains II and III are S1-like domains and have structural homology to the eIF5A domain C, suggesting that domains II and III evolved by duplication. This entry reresents the central domain of elongation factor P and its homologues. It forms an oligonucleotide-binding (OB) fold, though it is not clear if this region is involved in binding nucleic acids [].
