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The La protein functions redundantly with tRNA modification enzymes to ensure tRNA structural stability

Departments of Cell Biology and Molecular Biophysics and Biochemistry, Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut 06536, USA

Reprint requests to: Sandra L. Wolin, Departments of Cell Biology and Molecular Biophysics and Biochemistry, Howard Hughes Medical Institute, Yale University School of Medicine, 295 Congress Avenue, New Haven, CT 06536, USA; e-mail: sandra.wolin{at}yale.edu; fax: (203) 737-1761.

Although the La protein stabilizes nascent pre-tRNAs from nucleases, influences the pathway of pre-tRNA maturation, and assists correct folding of certain pre-tRNAs, it is dispensable for growth in both budding and fission yeast. Here we show that the Saccharomyces cerevisiae La shares functional redundancy with both tRNA modification enzymes and other proteins that contact tRNAs during their biogenesis. La is important for growth in the presence of mutations in either the arginyl tRNA synthetase or the tRNA modification enzyme Trm1p. In addition, two pseudouridine synthases, PUS3 and PUS4, are important for growth in strains carrying a mutation in tRNA^Arg_CCG and are essential when La is deleted in these strains. Depletion of Pus3p results in accumulation of the aminoacylated mutant tRNA^Arg_CCG in nuclei, while depletion of Pus4p results in decreased stability of the mutant tRNA. Interestingly, the degradation of mutant unstable forms of tRNA^Arg_CCG does not require the Trf4p poly(A) polymerase, suggesting that yeast cells possess multiple pathways for tRNA decay. These data demonstrate that La functions redundantly with both tRNA modifications and proteins that associate with tRNAs to achieve tRNA structural stability and efficient biogenesis.

Keywords: La protein; tRNA; tRNA modification; aminoacyl-tRNA synthetase; subcellular localization; RNA stability

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