title: Involvement of nuclear import and export factors in U8 box C/D snoRNP biogenesis.
abstract: Box C/D snoRNPs, factors essential for ribosome biogenesis, are proposed to be assembled in the nucleoplasm before localizing to the nucleolus. However, recent work demonstrated the involvement of nuclear export factors in this process, suggesting that export may take place. Here we show that there are distinct distributions of U8 pre-snoRNAs and pre-snoRNP complexes in HeLa cell nuclear and cytoplasmic extracts. We observed differential association of nuclear export (PHAX, CRM1, and Ran) factors with complexes in the two extracts, consistent with nucleocytoplasmic transport. Furthermore, we show that the U8 pre-snoRNA in one of the cytoplasmic complexes contains an m3G cap and is associated with the nuclear import factor Snurportin1. Using RNA interference, we show that loss of either PHAX or Snurportin1 results in the incorrect localization of the U8 snoRNA. Our data therefore show that nuclear export and import factors are directly involved in U8 box C/D snoRNP biogenesis. The distinct distribution of U8 pre-snoRNP complexes between the two cellular compartments together with the association of both nuclear import and export factors with the precursor complex suggests that the mammalian U8 snoRNP is exported during biogenesis.
authors: Institute for Cell and Molecular Biosciences, University of Newcastle, Newcastle upon Tyne NE2 4HH, United Kingdom. n.j.watkins@ncl.ac.uk
authors: Nicholas J
authors: NJ
authors: Watkins
authors: Ira
authors: I
authors: Lemm
authors: Reinhard
authors: R
authors: Lührmann
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000502:physiology*; D000818:Animals; D001483:Base Sequence; D002458:Cell Fractionation; D002467:Cell Nucleus / Q000737:chemistry / Q000378:metabolism; D003593:Cytoplasm / Q000737:chemistry / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D029543:Nucleocytoplasmic Transport Proteins / Q000235:genetics / Q000378:metabolism; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D039381:RNA Cap-Binding Proteins / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism; D020718:Ribonucleoproteins, Small Nucleolar / Q000235:genetics / Q000378:metabolism*
chemical_list: D029543:Nucleocytoplasmic Transport Proteins; C498688:PHAX protein, human; D010750:Phosphoproteins; D039381:RNA Cap-Binding Proteins; D018160:Receptors, Cytoplasmic and Nuclear; D020718:Ribonucleoproteins, Small Nucleolar; C114090:SNUPN protein, human
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