Identification of an altered elongation factor in temperature-sensitive mutant ts 7'-14 of Saccharomyces cerevisiae

The ribosomal 5.8S RNA as a target site for p53 protein in cell differentiation and oncogenesis

Previous studies have shown that the ribosomal 5.8S rRNA of human cells is partially methylated in a tissue-specific fashion, a modification which occurs largely or entirely in the cytoplasm. More recent studies have shown that the 5.8S rRNA forms a covalent linkage with tumor suppressor p53 protein and have suggested that this RNA plays a functional role in protein elongation. We now show that the expression of p53 protein in Schizosaccharomyces pombe results in cells which: morphologically resemble transformed cells expressing mutant 5.8S rRNA; are equally compromised in their ability to sustain protein synthesis, in vitro; and contain polyribosome profiles which strongly resemble the elevated profiles which also are observed with mutated 5.8S rRNA. Taken together, these results provide new physiological evidence of the possibility that the 5.8S rRNA is an important target in the control of ribosome function during cell differentiation and oncogenesis.

Overexpression and purification of elongation factor 3 from Saccharomyces cerevisiae

The translational elongation factor 3 (EF-3) from Saccharomyces cerevisiae was overexpressed and purified to near homogeneity from the post-ribosomal supernatant fraction (S-100). A detailed protocol for the isolation of overexpressed EF-3 is presented. The procedure involves ion-exchange chromatography on DEAE-Sepharose and CM-Sepharose and affinity chromatography on ATP-agarose. A protein purity of > or = 96% was established by quantitating the silver-stained SDS/polyacrylamide gel. The present method facilitates isolation of EF-3 in large amounts in high yield.

Isolation and sequence analysis of the gene encoding translation elongation factor 3 from Candida albicans

The structural gene encoding translation elongation factor 3 (EF-3) has been cloned from a Candida albicans genomic library by hybridization to a Saccharomyces cerevisiae probe containing the Saccharomyces gene, YEF3 (Sandbaken et al., 1990b). The sequences were shown to be functionally homologous to the Saccharomyces gene by three criteria: (1) a Saccharomyces strain transformed with a high copy plasmid containing CaEF3 sequences overproduces the EF-3 peptide two-fold; (2) extracts from this strain exhibit a two-fold increase in the EF-3-catalysed, ribosome-dependent ATPase activity (Kamath and Chakraburtty, 1988); and (3) the Candida gene complements a Saccharomyces null mutant. The coding region, identified by DNA sequencing, indicates that CaEF3 encodes a 1050 amino acid polypeptide having a potential molecular weight of 116,865 Da. This protein shows 77% overall identity to the Saccharomyces YEF3 gene, with a significantly greater identity (94%) concentrated in the region of the protein thought to contain the catalytic domain of EF-3 (Sandbaken et al., 1990a). The upstream non-coding region contains T-rich regions typical of many yeast genes and several potential RAP1/GRF1 elements shown to regulate expression of a number of translational genes (Mager, 1988). The data confirm a high degree of conservation for EF-3 among the two organisms.

Elongation factor 3 (EF-3) from Candida albicans shows both structural and functional similarity to EF-3 from Saccharomyces cerevisiae

As with many other fungi, including the budding yeast Saccharomyces cerevisiae, the dimorphic fungus Candida albicans encodes the novel translation factor, elongation factor 3 (EF-3). Using a rapid affinity chromatography protocol, EF-3 was purified to homogeneity from C. albicans and shown to have an apparent molecular mass of 128 kDa. A polyclonal antibody raised against C. albicans EF-3 also showed cross-reactivity with EF-3 from S. cerevisiae. Similarly, the S. cerevisiae TEF3 gene (encoding EF-3) showed cross-hybridization with genomic DNA from C. albicans in Southern hybridization analysis, demonstrating the existence of a single gene closely related to TEF3 in the C. albicans genome. This gene was cloned by using a 0.7 kb polymerase chain reaction-amplified DNA fragment to screen to C. albicans gene library. DNA sequence analysis of 200 bp of the cloned fragment demonstrated an open reading frame showing 51% predicted amino acid identity between the putative C. albicans EF-3 gene and its S. cerevisiae counterpart over the encoded 65-amino-acid stretch. That the cloned C. albicans sequence did indeed encode EF-3 was confirmed by demonstrating its ability to rescue an otherwise non-viable S. cerevisiae tef3:HIS3 null mutant. Thus EF-3 from C. albicans shows both structural and functional similarity to EF-3 from S. cerevisiae.

Isolation and characterization of the structural gene encoding elongation factor 3

The unique yeast translational factor EF-3 participates in the elongation cycle by stimulating the function of EF-1 alpha in binding aminoacyl-tRNA to the ribosome. We have isolated the structural gene encoding EF-3 from the yeast Saccharomyces cerevisiae. The YEF3 gene is found in one copy per haploid genome and is essential for vegetative growth. DNA sequence analysis reveals that the YEF3 gene contains an open reading frame of 1044 codons. The deduced amino acid sequence has two repeats of a nucleotide-binding motif. Each of these repeats shows similarity to the nucleotide-binding motif of hydrophilic, membrane-associated ATPases including human multidrug resistant protein MDR. Factor 3 manifests ribosome-dependent ATP hydrolysis. Introduction of the YEF3 gene on a high copy number plasmid into yeast strains increases the ribosome-dependent ATPase activity and EF-3 protein levels by 3-5-fold. Yeast strains containing elevated EF-3 protein levels also exhibit increased sensitivity to the aminoglycoside antibiotics hygromycin and paromomycin. These drugs are known to increase translational errors. These observations suggest that EF-3 may affect translational accuracy.

Yeast, Saccharomyces cerevisiae, cell-free translation: the inhibition of translation by high temperature is reversible

Yeast, Saccharomyces cerevisiae, extracts are inactive for translation at 37 degrees C. Two unexplained, simultaneously occurring phenomena appear to be responsible for this effect: (i) rapid inhibition of translation, and (ii) time-dependent inactivation of (a) translational component(s) at 37 degrees C. After short incubation of an extract at 37 degrees C, protein synthesis recovers efficiently after transfer of the extract to 23 degrees C. This behaviour of yeast cell-free systems enables the in vitro inactivation of temperature-sensitive translational components and therefore facilitates studies with extracts derived from temperature-sensitive strains.