Role of Pseudouridine Formation by Deg1 for Functionality of Two Glutamine Isoacceptor TRNAs

Loss of Deg1/Pus3 and concomitant elimination of pseudouridine in tRNA at positions 38 and 39 (ψ38/39) was shown to specifically impair the function of tRNA under conditions of temperature-induced down-regulation of wobble uridine thiolation in budding yeast and is linked to intellectual disability in humans. To further characterize the differential importance of the frequent ψ38/39 modification for tRNAs in yeast, we analyzed the in vivo function of non-sense suppressor tRNAs and in the absence of the modifier. In the tRNA variant , UAA read-through is enabled due to an anticodon mutation (UψA), whereas is a mutant form of tRNA () that mediates UAG decoding due to a mutation of the anticodon-loop closing base pair (G31:C39 to A31:C39). While function is unaltered in mutants, the ability of to mediate non-sense suppression and to complement a genomic deletion of the essential gene is severely compromised. These results and the differential suppression of growth defects in mutants by multi-copy or are consistent with the interpretation that ψ38 is most important for tRNA function under heat stress but becomes crucial for tRNA as well when the anticodon loop is destabilized by the mutation. Thus, ψ38/39 may protect the anticodon loop configuration from disturbances by loss of other modifications or base changes.