Identification of genes important for biogenesis of tRNA ^Ser/CGA.
Marcus J. O. Johansson, Anders S. Byström
Dept. of Molecular Biology, Umeå University, Building 6L, Umeå, 901 87, Sweden (anders.bystrom@molbiol.umu.se)

A 5-methyluridine (m⁵U) residue at position 54 is a conserved feature of bacterial and eukaryotic tRNAs. The methylation of U₅₄ is catalysed by the tRNA(m⁵U₅₄)methyltransferase, which in Saccharomyces cerevisiae is encoded by the nonessential TRM2 gene. We have identified four different strains with mutant forms of a single copy and essential tRNA^Ser/CGA gene that in the absence of the TRM2 gene induces lethality. In these strains the stability of tRNA^Ser/CGA is decreased. Two alleles of TRM2 encoding catalytically inactive tRNA(m⁵U₅₄)methyltransferases were able to stabilise tRNA^Ser/CGA in one of the mutants, revealing a role for the Trm2 protein per se in tRNA maturation. Other tRNA modification enzymes interacting with tRNA^Ser/CGA in the maturation process, such as Pus4p, Trm1p and Trm3p were essential or important for growth of the tRNA^Ser/CGA mutants. Moreover, Lhp1p a protein binding RNA polymerase III transcripts was required to stabilise the mutant tRNAs. With this knowledge we have used a strain with one of the tRNA^Ser/CGA genes mutated and screened for mutations that generates lethality. These mutations have identified genes that are important for the biogenesis of tRNA^Ser/CGA.

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