Varied forms of mutant tRNA mistranslation produce distinct phenotypes across multiple model organisms

Mutant tRNA mistranslation is a phenomena in which specific tRNA gene mutations cause translational errors wherein amino acids incorporated during translation differ from those coded by mRNA sequences. The biological consequences of mutant tRNA mistranslation are highly complex and contextual, but are often deleterious. Importantly, many variables exist that are likely to affect the outcomes of any one mutant mistranslating tRNA; biochemical characteristics of the exchanged amino acids, frequency of use, identity of mistranslated products, and so on. Here, we generate a carefully curated array of tRNA mutants to assess which characteristics of mistranslating tRNA variants are most predictive of deleterious phenotypes. We find that toxicity often arises from mutant tRNAs that induce dramatic changes in biochemical properties between exchanged amino acids, as well as mistranslation that occurs more frequently. Importantly, exceptions are also observed to each of these general rules, implying instead that some deliriousness may arise from more granular, product-specific mechanisms. Additionally, quantification of mistranslation via mass spectrometry demonstrates a weak relationship between quantity of mistranslated products and severity of toxic phenotypes. Lastly, despite previous establishment of mutant mistranslating tRNA models in Drosophila melanogaster, incorporation of higher frequency mistranslating tRNA variants was largely unsuccessful, and incorporation of lower frequency mistranslating tRNA variants produces no detectable developmental phenotypes. These experiments support the notion that although general rules may be capable of reasonably predicting their consequences, each mistranslating tRNA variant warrants individual consideration and investigation for thorough understanding of its biological outcomes and precise mechanisms of toxicity.