Elongation factors belong to a family of proteins that promote the GTP-dependent binding of aminoacyltRNA to the A site of ribosomes during protein biosynthesis, and catalyse the translocation of thesynthesised protein chain from the A to the P site. The proteins are all relatively similar in the vicinity oftheir C-termini, and are also highly similar to a range of proteins that includes the nodulation Q protein from<taxon tax_id="382">Rhizobium meliloti</taxon> (Sinorhizobium meliloti), bacterial tetracycline resistance proteins [<cite idref="PUB00002069"/>] and yeast elongation factors.<p>Although the yeast elongation factors, or omnipotent suppressor proteins,share a large degree of similarity with other eukaryotic elongation factors, the chief difference is that they possess an N-terminal extension rich in repetitive, glutamine-rich elements, and a central charged unit. <taxon tax_id="4932">Saccharomyces cerevisiae</taxon> ERF2 expression has been shown to cause non-mendelian (all progeny to the first and second generation exhibit the phenotype) inheritance of nonsense suppression (stop-codon read-through), mediated by the N-terminal and charged regions. This observation has led to the hypothesis that the yeast elongation factors are yeast prions', showing the same properties as those theorised to exist in mammalian prions [<cite idref="PUB00008070"/>].</p>