Quality control mechanisms in the tRNA anticodon loop


Eric PhizickyUniversity of Rochester Medical School, USA.

Abstract: Work in our lab focuses on tRNA biogenesis, function, and quality control mechanisms in eukaryotes, with an emphasis on the yeast Saccharomyces cerevisiae. tRNA biogenesis is crucial in all organisms, and involves multiple steps, including end processing, splicing, formation of numerous post-transcriptional modifications, and precisely controlled intracellular trafficking. Mutations in genes involved in tRNA biogenesis often have profound consequences, leading to cell death, distinct growth defects, or translational defects in yeast, and to a number of neurological and other disorders in humans, including pontocerebellar hypoplasia, familial dysautonomia, intellectual disability, microcephaly, and several mitochondrial diseases. We are studying the mechanisms by which quality control is maintained during and after tRNA biogenesis in S. cerevisiae, and how some of these pathways are extended in the distantly related yeast Schizosaccharomyces pombe and in human cell lines. One major current topic focuses on the biology of selected anticodon loop modifications in yeast and humans, and on recognition of tRNA substrates for modification.

About the speaker: My graduate work focused on recA protein-mediated proteolytic cleavage of lambdoiod phage repressors during SOS induction in E. coli. I used kinetic analysis to provide evidence that the λ repressor monomer was the true substrate, and that cleavage correlated with the efficiency of a RecA/ssDNA/NTP complex. I have studied tRNA for more than 30 years, with an emphasis on tRNA processing steps and tRNA biology in the yeast Saccharomyces cerevisiae. My postdoctoral work focused on purification of the tRNA splicing ligase, cloning of the gene, and analysis of its role in splicing in vivo. Subsequent work in my lab began with identification, characterization, and purification of the 2'-phosphotransferase that removes the splice junction 2'-phosphate, demonstration that the phosphate is transferred to NAD to form the novel metabolite ADP-ribose 1"-2" cyclic phosphate (Appr>p), cloning of the gene, and analysis of the mechanism and specificity of the reaction. Using the biochemical genomics approach described below and other methods, my lab identified 15 additional genes encoding enzymes involved in tRNA processing, including a specific cyclic phosphodiesterase and phosphatase that metabolize Appr>p, components of 7 tRNA methyltransferases (8 genes) that catalyze formation of Nm4, m1G9, m3C32, Cm32, Nm34, Um44, and m7G46 on tRNAs, four dihydrouridine synthases that modify specific uridine residues of tRNAs, and the tRNAHis guanylyltransferase that adds G-1 to the 5' end of tRNAHis (which we also discovered acts as a 3'-5' reverse polymerase). 

Location: Amphi Charpak (LPNHE), ground floor, tower 22, Jussieu Campus.

Eric Phizicky's lab website