Physiological significance of the two isoforms of initiator tRNAs in .

Unlabelled: possesses four initiator tRNA (i-tRNA) genes, three of which are present together as and the fourth one as . In B, all four genes ( and ) encode i-tRNA, in which the G at position 46 is modified to mG46 by TrmB (mG methyltransferase). However, in K, because of a single-nucleotide polymorphism, encodes a variant, i-tRNA, having an A in place of mG46. We generated strains to explore the importance of this polymorphism in i-tRNAs. The strains were sustained either on ( of K origin encoding i-tRNA) or its derivative (encoding i-tRNA) in single (chromosomal) or plasmid-borne copies. We show that the strains sustained on i-tRNA have a growth fitness advantage over those sustained on i-tRNA. The growth fitness advantages are more pronounced for the strains sustained on i-tRNA in nutrient-rich media than in nutrient-poor media. The growth fitness of the strains correlates well with the relative stabilities of the i-tRNAs . Furthermore, the atomistic molecular dynamics simulations support the higher stability of i-tRNA than that of i-tRNA. The stability of i-tRNA remains unaffected upon the deletion of TrmB. These studies highlight how and alleles might influence the growth fitness of under certain nutrient-limiting conditions.

Importance: harbors four initiator tRNA (i-tRNA) genes: three of these at and the fourth one at loci. In B, all four genes encode i-tRNA. In K, because of a single-nucleotide polymorphism, metY encodes a variant, i-tRNA, having an A in place of G at position 46 of i-tRNA sequence in metY. We show that G46 confers stability to i-tRNA. The strains sustained on i-tRNA have a growth fitness advantage over those sustained on i-tRNA. Strains harboring (B mimic) or (K mimic) show that while in the nutrient-rich media, the K mimic is outcompeted rapidly; in the nutrient-poor medium, the K mimic is outcompeted less rapidly.