tRNA Mimicry in RNA Regulation of Gene Expression

Aminoacyl tRNA synthetases are a well-studied family of enzymes with a canonical role in charging tRNA with specific, cognate, amino acid. Yet, these proteins appear to exert non-canonical roles, including post-transcriptional regulation of mRNA expression.

Ore data revealed that ThrRS interacts with mRNA containing an anticodon stem-loop (ASL) element. This mRNA encodes to RPC10, a subunit of RNA polymerase III. We found that mutations that abolish the predicted ASL-like structure and sequence significantly lower binding to ThrRS and reduced RPC10 protein level. Concomitantly, tRNAThr levels were significantly reduced in the mutated strain. These data uncover a novel regulatory mechanism, in which tRNA levels are regulated through a mimicking element.

Additionally, we found that MetRS-bound regions were significantly enriched with sites that were previously described to contain pseudouridine (Ψ). Analysis of a prime target, Translation elongation factor 3 (YEF3) mRNA position 1074, revealed the importance of pseudouridine for MetRS interaction both in-vitro and in-vivo. Moreover, western and polysomal analyses uncovered that MetRS regulate the translation of Yef3p, a fungus-specific translation factor that has a role in ribosome recycling and assisting ribosomes’ movement along the ORF. Pseudouridylation of YEF3 mRNA is presumably mediated by Pus6, a specific tRNAMet pseudouridine synthetase. Consistently, Pus6 knockout decrease MetRS interaction with both tRNAMet and YEF3 mRNA. Furthermore, while pus6 knockout resulted in global protein translation reduction, YEF3-specific translation increased.

Together, our research reveals a novel post-transcriptional regulatory mechanism that exploits structure and modification mimicry to control mRNA translation according to tRNA demands.