A 5-methyluridine (m5U) residue at position 54 is a conserved
feature of bacterial and eukaryotic tRNAs. The methylation of U54
is catalyzed by the tRNA(m5U54)methyltransferase,
which in Saccharomyces cerevisiae is encoded by the nonessential
TRM2 gene. In this study, we identified four different strains with
mutant forms of tRNACGASer.
The absence of the TRM2 gene in these strains decreased the
stability of tRNACGASer
and induced lethality. Two alleles of TRM2 encoding
catalytically inactive tRNA(m5U54)methyltransferases
were able to stabilize tRNACGASer in one of the
mutants, revealing a role for the Trm2 protein per se in tRNA maturation.
Other tRNA modification enzymes interacting with
tRNACGASer in the maturation process, such as Pus4p,
Trm1p, and Trm3p were essential or important for growth of the
tRNACGASer
mutants. Moreover, Lhp1p, a protein binding RNA polymerase III
transcripts, was required to stabilize the mutant tRNAs. Based
on our results, we suggest that tRNA modification enzymes might
have a role in tRNA maturation not necessarily linked to their
known catalytic activity.