Poster abstracts
Poster number 131 submitted by Paolo Sinopoli
Free tRNA introns act as novel noncoding regulatory RNAs
Paolo L. Sinopoli (Department of Molecular Genetics & Center for RNA Biology, The Ohio State University), Regina T. Nostramo (Department of Molecular Genetics & Center for RNA Biology, The Ohio State University), Alicia Bao (Department of Molecular Genetics & Center for RNA Biology, The Ohio State University), Sara Metcalf (Department of Molecular Genetics & Center for RNA Biology, The Ohio State University), Anita K. Hopper (Department of Molecular Genetics & Center for RNA Biology, The Ohio State University)
Abstract:
tRNAs are created through transcription of tRNA genes, a subset of which contain introns that are excised during tRNA maturation. tRNA intron sequences are highly conserved between closely related species within Drosopholid and Saccharomycetaceae families, yet there is no known sequence-dependent role for tRNA introns. We report that the sequences of tRNA introns in Saccharomyces cerevisiae have remarkable and statistically improbable regions of complementarity to coding open reading frames (ORFs) of mRNAs. Contrastingly, tRNA exons have none or minimal complementarity to ORFs. The data lead us to propose that tRNA introns might interact with mRNA sequences similarly to regulatory microRNAs that are found in other organisms. To test this hypothesis, we generated a strain that lacks the tRNAIle introns from both tRNAIle genes (IleiΔ). In the IleiΔ strain, there are significant increases in levels of mRNAs with complementarity to the tRNAIle intron, but not for mRNAs lacking complementarity. Congruently, inducible overexpression of the tRNAIle intron results in a reduction of mRNAs with complementarity to the intron relative to mRNAs lacking complementarity. Further, mutations of yeast genes that accumulate tRNA introns also display reductions in the levels of mRNAs with complementarity to tRNA introns. Together, the data indicate that tRNA introns possess complementarity-dependent inhibitory effects on mRNA levels. This inhibitory effect is dependent on nuclear and cytoplasmic ribonucleases, indicating direct action of tRNA introns on mRNA stability. Levels of mRNAs with tRNA intron complementarity in their UTRs are unaffected in our experiments, differentiating regulation by tRNA introns from microRNAs. This is consistent with S. cerevisiae lacking the argonaute proteins integral to microRNA function, indicating that mRNA regulation by tRNA introns occurs through an alternative, currently unknown, mechanism. Our findings lead us to propose that free introns of tRNAs act as a new class of small regulatory RNAs.
References:
Nostramo RT, Sinopoli PL, Bao A, Metcalf S, Peltier LM, Hopper AK. FitRNA for duty: Free introns of tRNAs as novel complementarity-dependent regulators of gene expression. In revision, Molecular Cell.
Keywords: tRNA, tRNA introns, regulatory RNA