Nup100 regulates Saccharomyces cerevisiae replicative life span by mediating the nuclear export of specific tRNAs

Nuclear pore complexes (NPCs), which are composed of nucleoporins (Nups) and regulate transport between the nucleus and cytoplasm, significantly impact the replicative life span (RLS) of Saccharomyces cerevisiae. We previously reported that deletion of the nonessential gene NUP100 increases RLS, although the molecular basis for this effect was unknown. In this study, we find that nuclear tRNA accumulation contributes to increased longevity in nup100 Delta cells. Fluorescence in situ hybridization (FISH) experiments demonstrate that several specific tRNAs accumulate in the nuclei of nup100 Delta mutants. Protein levels of the transcription factor Gcn4 are increased when NUP100 is deleted, and GCN4 is required for the elevated life spans of nup100. mutants, similar to other previously described tRNA export and ribosomal mutants. Northern blots indicate that tRNA splicing and aminoacylation are not significantly affected in nup100 Delta cells, suggesting that Nup100 is largely required for nuclear export of mature, processed tRNAs. Distinct tRNAs accumulate in the nuclei of nup100 Delta and msn5 Delta mutants, while Los1-GFP nucleocytoplasmic shuttling is unaffected by Nup100. Thus, we conclude that Nup100 regulates tRNA export in a manner distinct from Los1 or Msn5. Together, these experiments reveal a novel Nup100 role in the tRNA life cycle that impacts the S. cerevisiae life span.