Evolution of robustness to protein mistranslation by accelerated protein turnover

To investigate how organisms mitigate the deleterious effects of mistranslation during evolution, a mutant tRNA was expressed in S. cerevisiae. The expression of Candida Ser-tRNACAG from a low copy plasmid in S. cerevisiae promoted mistranslation events by random incorporation of both serine and leucine at CUG codons. As mistranslation causes an overload of the protein quality pathways, it disrupts cellular protein homeostasis leading to a major fall in fitness. Laboratory evolutionary experiments were performed to study whether the fitness cost of mistranslation can be lowered. We also wanted to identify the cost-reduction strategy: reducing the frequencies of errors (mitigation), or increasing tolerance to errors (robustness), either by global or local activities. Gene expression was measured in the ancestor (non-evolved) lineage in two different situations: 1) carrying an empty vector and 2) expressing the mutant Ser-tRNACAG. Gene expression was also measured in three ambiguously evolved lineages (B3, D11, H9) in both situations (carrying an empty vector and expressing the mutant tRNA). Three independent experiments were performed for each lineage. Non-evolved strain with empty vector was used as control sample.