title: Gemin8 is a novel component of the survival motor neuron complex and functions in small nuclear ribonucleoprotein assembly.
abstract: The survival motor neuron (SMN) protein is the product of the spinal muscular atrophy disease gene. SMN and Gemin2-7 proteins form a large macromolecular complex that localizes in the cytoplasm as well as in the nucleoplasm and in nuclear Gems. The SMN complex interacts with several additional proteins and likely functions in multiple cellular pathways. In the cytoplasm, a subset of SMN complexes containing unrip and Sm proteins mediates the assembly of spliceosomal small nuclear ribonucleoproteins (snRNPs). Here, by mass spectrometry analysis of SMN complexes purified from HeLa cells, we identified a novel protein that is evolutionarily conserved in metazoans, and we named it Gemin8. Co-immunoprecipitation and immunolocalization experiments demonstrated that Gemin8 is associated with the SMN complex and is localized in the cytoplasm and in the nucleus, where it is highly concentrated in Gems. Gemin8 interacts directly with the Gemin6-Gemin7 heterodimer and, together with unrip, these proteins form a heteromeric subunit of the SMN complex. Gemin8 is also associated with Sm proteins, and Gemin8-containing SMN complexes are competent to carry out snRNP assembly. Importantly, RNA interference experiments indicate that Gemin8 knock-down impairs snRNP assembly, and Gemin8 expression is down-regulated in cells with low levels of SMN. These results demonstrate that Gemin8 is a novel integral component of the SMN complex and extend the repertoire of cellular proteins involved in the pathway of snRNP biogenesis.
authors.affiliation: Dulbecco Telethon Institute, Institute of Cell Biology, Consiglio Nazionale delle Ricerche, 00016 Monterotondo Scalo, Rome, Italy.
authors.forename: Claudia
authors.initials: C
authors.lastname: Carissimi
authors.forename: Luciano
authors.initials: L
authors.lastname: Saieva
authors.forename: Jennifer
authors.initials: J
authors.lastname: Baccon
authors.forename: Pieranna
authors.initials: P
authors.lastname: Chiarella
authors.forename: Alessio
authors.initials: A
authors.lastname: Maiolica
authors.forename: Alan
authors.initials: A
authors.lastname: Sawyer
authors.forename: Juri
authors.initials: J
authors.lastname: Rappsilber
authors.forename: Livio
authors.initials: L
authors.lastname: Pellizzoni
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D002499:Centrifugation, Density Gradient; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism / Q000502:physiology*; D003593:Cytoplasm / Q000378:metabolism; D004247:DNA / Q000737:chemistry; D019281:Dimerization; D015536:Down-Regulation; D004591:Electrophoresis, Polyacrylamide Gel; D005982:Glutathione Transferase / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D047468:Immunoprecipitation; D051379:Mice; D008810:Mice, Inbred C57BL; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000378:metabolism / Q000502:physiology*; D009687:Nuclear Proteins / Q000096:biosynthesis* / Q000502:physiology*; D011485:Protein Binding; D034622:RNA Interference; D016601:RNA-Binding Proteins / Q000378:metabolism / Q000502:physiology*; D017411:Ribonucleoproteins, Small Nuclear / Q000737:chemistry*; D055532:SMN Complex Proteins; D017386:Sequence Homology, Amino Acid; D013395:Sucrose / Q000494:pharmacology
chemical_list: D017362:Cyclic AMP Response Element-Binding Protein; C510132:GEMIN8 protein, human; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D016601:RNA-Binding Proteins; D017411:Ribonucleoproteins, Small Nuclear; D055532:SMN Complex Proteins; D013395:Sucrose; D004247:DNA; D005982:Glutathione Transferase