The tRNA recognition mechanism of folate/FAD-dependent tRNA methyltransferase (TrmFO).

The conserved U54 in tRNA is often modified to 5-methyluridine (m(5)U) and forms a reverse Hoogsteen base pair with A58 that stabilizes the L-shaped tRNA structure. In Gram-positive and some Gram-negative eubacteria, m(5)U54 is produced by folate/FAD-dependent tRNA (m(5)U54) methyltransferase (TrmFO). TrmFO utilizes N(5),N(10)-methylenetetrahydrofolate (CH(2)THF) as a methyl donor.

Pseudouridine at position 55 in tRNA controls the contents of other modified nucleotides for low-temperature adaptation in the extreme-thermophilic eubacterium Thermus thermophilus.

Pseudouridine at position 55 (Ψ55) in eubacterial tRNA is produced by TruB. To clarify the role of the Ψ55 modification, we constructed a truB gene disruptant (ΔtruB) strain of Thermus thermophilus which is an extreme-thermophilic eubacterium. Unexpectedly, the ΔtruB strain exhibited severe growth retardation at 50 °C.

Atomic structure of a folate/FAD-dependent tRNA T54 methyltransferase.

tRNAs from all 3 phylogenetic domains have a 5-methyluridine at position 54 (T54) in the T-loop. The methyl group is transferred from S-adenosylmethionine by TrmA methyltransferase in most Gram-negative bacteria and some archaea and eukaryotes, whereas it is transferred from 5,10-methylenetetrahydrofolate (MTHF) by TrmFO, a folate/FAD-dependent methyltransferase, in most Gram-positive bacteria and some Gram-negative bacteria. However, the catalytic mechanism remains unclear, because the crystal structure of TrmFO has not been solved.

Amount changes of tRNA modification enzymes in Thermus thermophilus HB8 cells according to culture temperatures.

Thermus thermophilus HB8 is an extreme thermophilic eubacrium, which grows at 50-80 degrees C. Transfer RNA molecules in T. thermophilus HB8 contains modified nucleosides such as Gm18, m(7)G46, m(5)s(2)U54, Psi55, and m(1)A58.