Modifications in the T arm of tRNA globally determine tRNA maturation, function and cellular fitness

All elongator tRNAs harbor 5-methyluridine 54 and pseudouridine 55 in the T arm, which are generated by the enzymes TrmA and TruB, respectively. Escherichia coli TrmA and TruB both act as tRNA chaperones, and strains lacking trmA or truB are outcompeted by wildtype. Here, we investigate how TrmA and TruB contribute to cellular fitness. Deletion of trmA and truB in E. coli causes a global decrease in aminoacylation and alters other tRNA modification such as acp3U47. Whereas overall protein synthesis is not affected in {Delta}trmA and {Delta}truB strains, the translation of a specific subset of codons is significantly impaired, and the expression of many specific proteins is translationally changed. In conclusion, we demonstrate that universal modifications of the tRNA T arm are critical for global tRNA function by enhancing tRNA maturation, tRNA aminoacylation, and translation, thereby improving cellular fitness and explaining trmA and truB conservation.