Modifications in the T arm of tRNA globally determine tRNA function and cellular fitness
Abstract: tRNAs are highly modified in the elbow region and harbor 5-methyluridine at position 54 and pseudouridine at position 55 in the T arm, which are generated by the enzymes TrmA and TruB, respectively. Although all elongator tRNAs contain these modifications across all domains of life, the cellular relevance of these modifications and their corresponding modifying enzymes remains elusive. In addition to modifying every tRNA, Escherichia coli TrmA and TruB have both been shown to fold tRNA independently of its modification activity acting as tRNA chaperones, and strains lacking trmA or truB are outcompeted by wildtype. To identify how TrmA and TruB contribute to cellular fitness, we have systematically assessed the effects of deleting trmA and/or trmB in E. coli. Since tRNA folding is a pre-requisite for tRNA aminoacylation, we determined cellular aminoacylation levels revealing a global decrease in aminoacylation for all tRNAs in ?trmA and ?truB. Moreover, the absence of 5-methyluridine 54 or pseudouridine 55 alters tRNA modification at other positions: whereas acp3U47 is decreased, thiouridine levels are increased. Understanding the importance of TrmA and TruB for tRNA aminoacylation and modification, we then analyzed how these global tRNA changes in ?trmA and ?truB strains affect translation. Whereas global protein synthesis is not significantly changed in ?trmA and ?truB, the abundances of many specific proteins are altered, and transcriptomics experiments suggest that the dysregulation of many proteins is controlled at the translational level. In conclusion, we demonstrate that universally conserved modifications of the tRNA elbow are critical for global tRNA function by enhancing other tRNA modifications, tRNA folding, tRNA aminoacylation and translation of specific genes thereby contributing to cellular fitness. Overall design: In order to compare the fraction of aminoacylated tRNA between ?trmA, ?truB, and ?trmA?truB Escherichia coli strains and the parental strain, E. coli BW25113, tRNA-seq was performed following ß-elimination of the 3'-A from uncharged tRNAs.