Poster abstracts
Poster number 14 submitted by Kunal Chatterjee
Biological significance of multiple, parallel primary tRNA nuclear export pathways in budding yeast
Kunal Chatterjee (Department of Molecular Genetics, The Ohio State University, Columbus, Ohio, U.S.A, Center for RNA Biology, The Ohio State University, Columbus, Ohio, U.S.A), Shubhra Majumder (Presidency University, Kolkata, West Bengal, India), Anita K.Hopper (Department of Molecular Genetics, The Ohio State University, Columbus, Ohio, U.S.A, Center for RNA Biology, The Ohio State University, Columbus, Ohio, U.S.A)
Abstract:
In eukaryotic cells, newly transcribed tRNAs are escorted out of the nucleus to the cytoplasm to participate in translation by the step termed primary tRNA nuclear export. Our recent work revealed that the mRNA exporter Mex67-Mtr2 heterodimer and possibly the protein exporter Crm1, co-function with the canonical tRNA nuclear exporter Los1 in this nuclear export process. Nuclear tRNA export by Los1 also provides an initial tRNA quality control step to generate functional tRNA, as Los1 preferentially binds to end-processed, appropriately structured tRNA. Thus, we sought to assess the fidelity of Los1-independent tRNA nuclear export pathways in yeast by three different approaches. First, we document that Los1-independent export pathways are error-prone, as enhanced levels of 5’–end unprocessed, spliced, non-functional tRNA accumulate in higher levels in los1Δ cells compared to wild-type cells. Second, Mex67-Mtr2 exhibits erroneous tRNA nuclear export, as 5’-end unprocessed, spliced tRNAs are detected in elevated levels in yeast cells under conditions in which Mex67 and Mtr2 are over-expressed. Third, in cells with mex67 or mtr2 mutations, the levels of aberrant tRNA are lower than wild-type cells after 2 h incubation at the non-permissive temperature, possibly because more tRNA are channeled through the high-fidelity Los1-mediated nuclear export pathway under these conditions. The question thus arises, why do cells employ multiple, parallel, but error-prone tRNA nuclear export pathways? We learned that environmental conditions can affect tRNA fidelity, likely due to the alternate use of various tRNA nuclear export pathways. We observed that elevated levels of aberrant m22G26 hypomodified tRNA are detected when yeast cells are grown above 30oC, but not at 23oC. Thus, yeast cells seem to employ the Los1-independent, error prone tRNA nuclear export pathways in varying environmental conditions, which may confer a yet unknown selective advantage to the cells in those situations.
Keywords: tRNA nuclear export, budding yeast, tRNA quality control