Disease relevance of SUP45

• A number of sal4 mutants were isolated and found to have pleiotropic, allele;specific phenotypes, including hypersensitivity in vivo to paromomycin and other antibiotics that stimulate translational errors in yeast [1].
• In contrast to Ra-eRF1, Tt-eRF1 formed aggregates upon overexpression in Escherichia coli, hence it was purified under denaturing conditions, and used to raise rabbit antibody [2].
• Two such proteins, Cdc37p and Sup45p, when overexpressed allowed partial relief of MPA toxicity, strongly suggesting that their lower amount after MPA treatment significantly contributed to the MPA effect [3].

High impact information on SUP45

• The yeast non-Mendelian factor [ETA+] is lethal in the presence of certain mutations in the SUP35 and SUP45 genes, which code for the translational release factors eRF3 and eRF1, respectively [4].
• The product of the yeast SUP45 gene (Sup45p) is highly homologous to the Xenopus eukaryote release factor 1 (eRF1), which has release factor activity in vitro [5].
• It is proposed that a quaternary complex composed of eRF1, eRF3, GTP and a stop codon of the mRNA is involved in termination of polypeptide synthesis in ribosomes [6].
• Omnipotent decoding potential resides in eukaryotic translation termination factor eRF1 of variant-code organisms and is modulated by the interactions of amino acid sequences within domain 1 [7].
• Collectively, these data suggest that variant genetic code organisms like Tetrahymena have an intrinsic potential to decode three stop codons in vivo, and that interaction within domain 1 between the KAT tripeptide and other sequences modulates the decoding specificity of Tetrahymena eRF1 [7].

Biological context of SUP45

• Guanidine reduces stop codon read-through caused by missense mutations in SUP35 or SUP45 [8].
• The transcription activation sites of SUP35 and SUP45 were mapped using deletion analysis of the respective promoter-reporter fusion genes [9].
• Chromosome stability in suppressor mutants for SUP35 and SUP45 genes coding for translation release factors was studied [10].
• A large amount of data have been produced, from which it was concluded that the SUP45 and SUP35 genes were controlling translation termination but were also involved in other functions important for the cell organization and the cell cycle accomplishment [11].
• The suppressor effect caused by overdosage of another gene, SUP45 (SUP1), is much lower and can be detected only for one construction which is derived from high copy number plasmid [12].

Anatomical context of SUP45

• We have demonstrated that ribosomes from the four suppressors SUP35, SUP44, SUP45 and SUP46 translate polyuridylate templates in vitro with higher errors than ribosomes from the normal stain, and that this misreading is substantially enhanced by the antibiotic paromomycin [13].
• A majority of sup35 and sup45 suppressor mutations confer supersensitivity to benomyl, the drug which de-polymerizes microtubules [14].
• Incubation in high salt concentrations (0.8 M KCl) suggested that the affinity of Sal4p for the 40S subunit was lower than that for monosomes or polysomes [15].
• Yeast polypeptide chain release factors eRF1 and eRF3 are involved in cytoskeleton organization and cell cycle regulation [16].
• Polypeptide chain termination in eukaryotic cells is mediated in part by the release factor eRF1 (Sup45p) [17].

Associations of SUP45 with chemical compounds

• Clearly, anti-suppression caused by growth in the presence of GuHCl is not sufficient to distinguish missense mutations in SUP35 or SUP45, from [PSI(+)] [8].
• The Saccharomyces cerevisiae RFs, mitochondrial Mrf1p and cytoplasmic Sup45p (eRF1), have sequence similarities to the bacterial RFs, including the potential site of glutamine methylation in the GGQ motif [18].
• Overproduced in S. cerevisiae, YDR140w can methylate eRF1 from yeast or man in vitro using S-adenosyl l-methionine as methyl donor provided that eRF3 and GTP are also present, suggesting that the natural substrate of the methyltransferase YDR140w is the ternary complex eRF1.eRF3.GTP [19].
• In each of four such allosuppressor alleles examined, an in-frame ochre (TAA) mutation was present in the SUP45 coding region; therefore each allele encoded both a truncated eRF1 protein and a full-length eRF1 polypeptide containing a serine missense substitution at the premature UAA codon [20].
• The Sal4p:ribosome association was only maintained when ribosomes were prepared in the presence of the translation elongation inhibitor cycloheximide; in uninhibited cells much lower levels of Sal4p were detectable in the 'run-off' polysomes [15].

Physical interactions of SUP45

• Two sites for Sup45p binding were found within Sup35p: one is formed by the N and M domains, and the other is located within the C domain [21].
• Yeast strains carrying a deletion of the TPA1 gene (tpa1Delta) exhibited increased readthrough of stop codons, and coimmunoprecipitation assays revealed that Tpa1p interacts with the translation termination factors eRF1 and eRF3 [22].

Regulatory relationships of SUP45

• We now show that SUP45 overexpression inhibits the induction of [PSI+] by Sup35p overproduction in [PIN+] strains, but has no effect on the propagation of [PSI+] or on the [PIN] status of the cells [23].

Other interactions of SUP45

• The products of the SUP45 (eRF1) and SUP35 genes interact to mediate translation termination in Saccharomyces cerevisiae [5].
• Thus, GuHCl must anti-suppress the sup35 and sup45 mutations via an in vivo target distinct from Hsp104 [8].
• In similar experiments, it was determined that Mtq2p methylates Sup45p [18].
• Thus, the gene products of SUP35, SUP44, SUP45 and SUP46 are components of the 40 S subunit or are enzymes that modify the subunit [13].
• Poly(A)-binding protein acts in translation termination via eukaryotic release factor 3 interaction and does not influence [PSI(+)] propagation [24].

Analytical, diagnostic and therapeutic context of SUP45

• Sequence analysis of Cl1 reveals that the corresponding protein is 67.5% identical (83% similar) to the product of the Saccharomyces cerevisiae SUP45 (also called SUP1 or SAL4) gene [25].
• By in vivo two-hybrid assay as well as by an in vitro pull-down analysis using purified proteins of S. pombe as well as of S. cerevisiae, eRF1 bound to the C-terminal one-third domain of eRF3, named eRF3C, but not to the N-terminal two-thirds, which was inconsistent with the previous report by Paushkin et al [26].
• By Northern blotting analysis the sizes of the transcripts were determined to be 1.6 kb for sup1 gene and 2.5 and 1.4kb for sup2 gene [27].
• Restriction mapping and DNA hybridisation analysis were used to demonstrate that the SAL4 gene is identical to the previously identified omnipotent suppressor gene SUP45 (SUP1) [1].
• Immunoprecipitations using 12CA5 antibodies and extracts from COS1 cells transiently transfected with eRF1 tagged with 9-amino acid epitope from influenza hemagglutinin (HA) demonstrated the presence of eRF1--PP2Acalpha--PR65alpha/Aalpha complex in these cells [28].

References