title: The homologous putative GTPases Grn1p from fission yeast and the human GNL3L are required for growth and play a role in processing of nucleolar pre-rRNA.
abstract: Grn1p from fission yeast and GNL3L from human cells, two putative GTPases from the novel HSR1_MMR1 GTP-binding protein subfamily with circularly permuted G-motifs play a critical role in maintaining normal cell growth. Deletion of Grn1 resulted in a severe growth defect, a marked reduction in mature rRNA species with a concomitant accumulation of the 35S pre-rRNA transcript, and failure to export the ribosomal protein Rpl25a from the nucleolus. Deleting any of the Grn1p G-domain motifs resulted in a null phenotype and nuclear/nucleolar localization consistent with the lack of nucleolar export of preribosomes accompanied by a distortion of nucleolar structure. Heterologous expression of GNL3L in a Deltagrn1 mutant restored processing of 35S pre-rRNA, nuclear export of Rpl25a and cell growth to wild-type levels. Genetic complementation in yeast and siRNA knockdown in HeLa cells confirmed the homologous proteins Grn1p and GNL3L are required for growth. Failure of two similar HSR1_MMR1 putative nucleolar GTPases, Nucleostemin (NS), or the dose-dependent response of breast tumor autoantigen NGP-1, to rescue deltagrn1 implied the highly specific roles of Grn1p or GNL3L in nucleolar events. Our analysis uncovers an important role for Grn1p/GNL3L within this unique group of nucleolar GTPases.
authors.affiliation: Laboratory of Nucleopore Biology, Institute of Molecular and Cell Biology, National University of Singapore, Singapore 117609, Singapore.
authors.forename: Xianming
authors.initials: X
authors.lastname: Du
authors.forename: Malireddi R K Subba
authors.initials: MR
authors.lastname: Rao
authors.forename: Xue Qin
authors.initials: XQ
authors.lastname: Chen
authors.forename: Wei
authors.initials: W
authors.lastname: Wu
authors.forename: Sundarasamy
authors.initials: S
authors.lastname: Mahalingam
authors.forename: David
authors.initials: D
authors.lastname: Balasundaram
mesh_terms: D021581:Active Transport, Cell Nucleus; D000595:Amino Acid Sequence; D002466:Cell Nucleolus / Q000235:genetics* / Q000378:metabolism*; D049109:Cell Proliferation; D017124:Conserved Sequence; D020558:GTP Phosphohydrolases / Q000737:chemistry / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D019204:GTP-Binding Proteins; D017353:Gene Deletion; D006367:HeLa Cells; D006801:Humans; D008958:Models, Molecular; D009154:Mutation / Q000235:genetics; D009687:Nuclear Proteins; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012322:RNA Precursors / Q000235:genetics*; D012269:Ribosomal Proteins / Q000235:genetics / Q000378:metabolism; D012568:Schizosaccharomyces / Q000166:cytology / Q000201:enzymology* / Q000235:genetics*; D029702:Schizosaccharomyces pombe Proteins / Q000737:chemistry / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment
chemical_list: C509155:GNL3L protein, human; D009687:Nuclear Proteins; D012322:RNA Precursors; D012269:Ribosomal Proteins; D029702:Schizosaccharomyces pombe Proteins; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; C509154:Grn1 protein, S pombe