A Los1p-independent pathway for nuclear export of intronless tRNAs in Saccharomycescerevisiae.
Los1p, the Saccharomyces cerevisiae exportin-t homologue, binds tRNA and functions in pre-tRNA splicing and export of mature tRNA from the nucleus to the cytosol. Because LOS1 is unessential in yeast, other pathways for tRNA nuclear export must exist. We report that Cca1p, which adds nucleotides C, C, and A to the 3' end of tRNAs, is a multicopy suppressor of the defect in tRNA nuclear export caused by los1 null mutations. Mes1p, methionyl-tRNA synthetase, also suppresses the defect in nuclear export of tRNA(Met) in los1 cells. Thus, Cca1p and Mes1p seem to function in a Los1p-independent tRNA nuclear export pathway. Heterokaryon analysis indicates that Cca1p is a nucleus/cytosol-shuttling protein, providing the potential for Cca1p to function as an exporter or an adapter in this tRNA nuclear export pathway. In yeast, most mutations that affect tRNA nuclear export also cause defects in pre-tRNA splicing leading to tight coupling of the splicing and export processes. In contrast, we show that overexpressed Cca1p corrects the nuclear export, but not the pre-tRNA-splicing defects of los1Kan(r) cells, thereby uncoupling pre-tRNA splicing and tRNA nuclear export.
Feng
Wenqin
W
Department of Biochemistry and Molecular Biology, H171, Pennsylvania State University College of Medicine, Hershey, PA 17033, USA.
Hopper
Anita K
AK
D021581:Active Transport, Cell Nucleus; D002467:Cell Nucleus / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism; D005656:Fungal Proteins / Q000378:metabolism; D049452:Green Fluorescent Proteins; D017404:In Situ Hybridization, Fluorescence; D008164:Luminescent Proteins / Q000378:metabolism; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D009154:Mutation; D028861:Nuclear Pore Complex Proteins / Q000378:metabolism*; D010957:Plasmids / Q000378:metabolism; D012316:RNA Nucleotidyltransferases / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D012343:RNA, Transfer / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D029702:Schizosaccharomyces pombe Proteins
D005656:Fungal Proteins; C408090:Los1 protein, S cerevisiae; D008164:Luminescent Proteins; C432695:Mes1 protein, S pombe; D028861:Nuclear Pore Complex Proteins; D012333:RNA, Messenger; D029701:Saccharomyces cerevisiae Proteins; D029702:Schizosaccharomyces pombe Proteins; D049452:Green Fluorescent Proteins; D004247:DNA; D012343:RNA, Transfer; D012316:RNA Nucleotidyltransferases; C023198:tRNA nucleotidyltransferase