Lost in Translation

Transfer RNAs (tRNAs) are small molecules that read the genetic code to build proteins inside cells. They undergo chemical modifications in their anticodon loops for optimizing translation speed, maintaining reading frame fidelity and preserving cellular protein balance. While individual tRNA modifications are often non-essential for basic viability, their combined absence can lead to severe physiological and translational defects. The Molecular Cell Biology Group (Ann Ehrenhofer-Murray) and the Molecular Microbiology Group (Marc Erhardt) demonstrated that the simultaneous loss of two specific anticodon-loop modifications (queuosine (Q34) and ms²i⁶A37/i⁶A37) on tRNA^Tyr causes severe growth defects, increased +1 frameshifting at tyrosine codons and enhanced protein aggregation in Escherichia coli. They showed that this functional interplay is evolutionarily conserved in Schizosaccharomyces pombe, where the loss of Q34 worsens the growth defects and rapamycin sensitivity of cells lacking i⁶A37. Overexpression of tRNA^Tyr rescues these defective phenotypes in both organisms, highlighting a critical synergistic role for Q34 and i⁶A37/ms²i⁶A in preserving translation fidelity and proteome stability. Read the Article in Nucleic Acids Research for more information.

Abstract

Queuosine (Q) modification at the wobble position (Q34) of tRNAs fine-tunes translational speed but is not essential for viability, leaving its physiological role unclear. In bacteria, Q34 is synthesized de novo, whereas eukaryotes obtain queuosine (Q) or its precursor queuine (q) from external sources. Q34 uniquely co-occurs with N⁶-isopentenyladenosine (i⁶A) or its derivative 2-methylthio-N⁶ isopentenyladenosine (ms²i⁶A) at position 37 of tRNA^Tyr. We show that loss of Q34 (∆tgt) causes a severe growth defect in Escherichia coli lacking ms²i⁶A due to deletion of the MiaA isopentenyltransferase (∆miaA), which is rescued by tRNA^Tyr overexpression. Simultaneous absence of Q34 and ms²i⁶A37 increases +1 frameshifting at tyrosine codons and promotes protein aggregation, indicating impaired tRNA^Tyr function. This functional interplay is evolutionarily conserved: Q34 deficiency aggravates the growth defect of Schizosaccharomyces pombe lacking the isopentenyltransferase Tit1 and thus i⁶A. In S. pombe, Q34 enhances tRNA^Tyr abundance in tit1∆ cells and reduces i⁶A37 levels in wild-type, revealing reciprocal regulation. Together, these findings demonstrate a synergistic role of Q34 and (ms²)i⁶A37 in maintaining translational fidelity and proteostasis, with potential implications for human health when Q availability is limited.