Nuclear RanGTP is not required for targeting small nucleolar RNAs to the nucleolus.
The small GTPase Ran is the central regulator of macromolecular transport between the cytoplasm and the nucleus. Recent work has suggested that RanGTP also plays an important role in regulating some intra-nuclear processes. In this study, we have investigated whether RanGTP is required for the intra-nuclear transport of RNAs. Specifically, we directly analyzed the nucleolar localization of Box C/D and Box H/ACA small nucleolar RNAs (snoRNAs) in mammalian (tsBN2) cells, Saccharomyces cerevisiae and Xenopus oocytes under conditions that deplete nuclear RanGTP and prevent RNA export to the cytoplasm. Our data suggest that depletion of nuclear RanGTP does not significantly alter the nucleolar localization of U3 snoRNA in tsBN2 cells. Complementary studies in the budding yeast S. cerevisiae using conditional Ran mutants as well as mutants in Ran regulatory proteins also indicate that disruption of the Ran gradient or of Ran itself does not detectably affect the nucleolar localization of snoRNAs. Finally, microinjection into Xenopus oocytes was used to clearly demonstrate that a specific pool of snoRNAs could still be efficiently targeted to the nucleolus even when the RanGTP gradient was disrupted by microinjection of mutant Ran proteins. Taken together, our data from three phylogenetically distinct experimental systems suggest that nuclear RanGTP, which is essential for trafficking of RNAs between the nuclear and cytoplasmic compartments, is not required for nuclear retention or nucleolar localization of snoRNAs.
Narayanan
Aarthi
A
Department of Biochemistry and Molecular Biology, University of Georgia, Life Sciences Building, Athens, GA 30602, USA.
Eifert
Julia
J
Marfatia
Kavita A
KA
Macara
Ian G
IG
Corbett
Anita H
AH
Terns
Rebecca M
RM
Terns
Michael P
MP
D021581:Active Transport, Cell Nucleus / Q000235:genetics*; D000818:Animals; D002451:Cell Compartmentation / Q000235:genetics; D018797:Cell Cycle Proteins; D002460:Cell Line; D002466:Cell Nucleolus / Q000201:enzymology* / Q000235:genetics; D006224:Cricetinae; D003593:Cytoplasm / Q000235:genetics / Q000378:metabolism; D005057:Eukaryotic Cells / Q000166:cytology / Q000201:enzymology*; D005260:Female; D005455:Fluorescent Antibody Technique; D015971:Gene Expression Regulation, Enzymologic / Q000235:genetics; D020662:Guanine Nucleotide Exchange Factors / Q000172:deficiency* / Q000235:genetics; D008845:Microinjections; D009154:Mutation / Q000235:genetics; D009687:Nuclear Proteins; D009865:Oocytes; D034443:RNA Transport / Q000235:genetics*; D020537:RNA, Small Nucleolar / Q000235:genetics / Q000378:metabolism*; D012440:Saccharomyces; D014981:Xenopus; D029867:Xenopus Proteins; D020931:ran GTP-Binding Protein / Q000172:deficiency* / Q000235:genetics
D018797:Cell Cycle Proteins; D020662:Guanine Nucleotide Exchange Factors; D009687:Nuclear Proteins; C499304:RCC1 protein, Xenopus; D020537:RNA, Small Nucleolar; C117378:RNA, U3 small nucleolar; D029867:Xenopus Proteins; D020931:ran GTP-Binding Protein