Evidence for a regulatory role of the evolutionarily conserved sequence complementarity between tRNAs

The tRNAs are non-coding RNAs (ncRNAs) known for their classical role in decoding mRNAs. Analysis of tRNA sequences from Escherichia coli revealed pairwise similarities for different combinations of tRNAs, as well as complementarities between some tRNA pairs. To explore the physiological significance of the complementarities between the tRNAs, we investigated the pair of tRNAs encoded by lysT (encoding an abundant tRNA, tRNA ^LysT ), and argU (encoding a rare tRNA, tRNA ^ArgU ). We show that tRNA ^LysT and tRNA ^ArgU anneal to form a heterodimer in vitro . The heterodimerisation is prevented by the presence of DNA oligomers complementary to the interacting sequences, in a dose dependent manner. Consistent with the notion of sequestration of tRNA ^ArgU by tRNA ^LysT , while the overexpression of tRNA ^ArgU did not impact the culture growth, that of tRNA ^LysT did. The tRNA ^LysT mediated inhibition of the culture growth was enhanced at a lower temperature. The AGA minigene (decoded by tRNA ^ArgU ) mediated toxicity and hybrid phage (λ _imm -P22) growth on Δ ssrA (tmRNA) strains was also consistent with the sequestration of tRNA ^ArgU by tRNA ^LysT . Also, we observed tRNA-derived fragments (tRFs) from tRNA ^LysT and tRNA ^ArgU , which too might facilitate tRNA ^ArgU sequestration. Taken together, these observations support a novel regulatory role of the evolutionary conserved complementarities between tRNAs.