Poster abstracts
Poster number 36 submitted by Kunal Chatterjee
Specific tRNAs Hijack mRNA Exporters For Nuclear Export
Kunal Chatterjee (Department of Molecular Genetics, Center for RNA Biology), Shubhra Majumder (Department of Molecular Genetics, Center for RNA Biology), Jingyan Wu (Department of Genetics, Stanford University), Anita K. Hopper (Department of Molecular Genetics, Center for RNA Biology)
Abstract:
tRNAs perform the essential role of delivering amino acids to the cytoplasmic protein synthesis machinery. To execute this role in protein production, eukaryotic tRNAs must be delivered out of the nucleus, their site of synthesis, to the cytoplasm, their site of function. Via the primary nuclear export step, newly transcribed, intron-containing, end matured, partially modified tRNAs are shuttled to the cytoplasm, where, in yeast, the tRNA splicing machinery is located. Genetic and biochemical studies have identified a set of RanGTPase binding proteins, “β-importins”, that are implicated in this tRNA movement. β-importin Los1 (Exportin-t) functions in primary tRNA nuclear export, but since it is unessential in every organism in which it has been ablated, there must be additional tRNA nuclear exporters that function in parallel to Los1. In a comprehensive screen, representing ~90% of the total yeast proteome, conducted recently in our laboratory, we uncovered novel genes involved in tRNA subcellular localization. Two such proteins, Mex67 and Mtr2, when inactivated, accumulate end-matured, unspliced tRNAs in cells, our proxy for defective tRNA nuclear export or splicing. The Mex67-Mtr2 heterodimer complex is the principal yeast nuclear export factor for bulk mRNA and also contributes to ribosomal subunit nuclear export. I have shown that tRNAs accumulate in the nucleus of mex67 mutant cells. Moreover, overexpressed Mex67-Mtr2 heterodimer can substitute for Los1, in cells deleted for LOS1 . I am currently investigating whether Mex67-Mtr2 function directly in tRNA nuclear export by binding to tRNAs. Our data also indicate that this novel tRNA nuclear exporter preferentially exports a subset of pre-tRNA species, most likely due to it’s binding preference for certain secondary structures present in some tRNA introns. Thus our studies lead to the hypothesis that tRNAs may hijack the mRNA export machinery as an alternative pathway for nuclear export.
Keywords: tRNA nuclear export, tRNA subcellular dynamics, Yeast