Poster number 85 submitted by Katie Clark
tRNA family-specific turnover pathways and environmental stresses regulate tRNA intron degradation
Katherine Clark (Molecular Genetics, Ohio State University), Sara Metcalf (Molecular Genetics, Ohio State University), Alicia Bao (Molecular Genetics, Ohio State University), Lauren Peltier (Molecular Genetics, Ohio State University), Anita K. Hopper (Department of Molecular Genetics, Center for RNA Biology, OSU, Columbus, OH)
In S. cerevisiae, 10 tRNA families are encoded by intron-containing genes. Precursor tRNAs are processed into mature functional tRNAs via several steps, including intron removal by the tRNA splicing endonuclease complex. After splicing, free introns are rapidly and efficiently degraded. The mechanism for tRNA intron turnover has been delineated for two of the 10 families (Wu and Hopper 2014); tRNAIleUAU and tRNALeuCAA linear introns are degraded by the 5’ to 3’ exonuclease Xrn1 after 5’ phosphorylation by the tRNA ligase/kinase Rlg1. There are at least 4 additional pathways for the remaining 8 tRNA families: Rlg1-dependent/Xrn1-independent, Rlg1-independent/Xrn1-dependent, Xrn1 and Rlg1-independent, and an endonuclease-dependent pathway for the circular form of the tRNATrp intron. We identified several candidate genes encoding proteins that function in tRNA family-specific intron turnover. From the identified candidates, three pathways for intron degradation have been uncovered: 1) competing pathways, 2) parallel pathways, and 3) an endonuclease pathway. We also investigated the effects of various environmental stresses on tRNA intron levels and uncovered stress-specific, tRNA family-specific intron accumulation. Treatment of wild-type cells with 3mM H2O2 results in 15- and 8-fold elevations of tRNATrpCCA and tRNALeuCAA intron levels, respectively. Accumulation of these tRNA introns occurs immediately and is maintained for at least 2 hours, despite immediate termination of tRNA transcription upon oxidative stress. tRNA introns spliced from tRNASer GCU and tRNALys UUU initially accumulate with the addition of H2O2, but level out after 1 hour. Inversely, most tRNA intron levels decrease with 42 ̊ C heat treatment. Our studies provide insight into family-specific endogenous and stress-induced intron turnover pathways that indicate possible novel regulatory functions of tRNA introns.
Keywords: tRNA turnover, intron degradation, environmental stress