title: Characterization of human Smg5/7a: a protein with similarities to Caenorhabditis elegans SMG5 and SMG7 that functions in the dephosphorylation of Upf1.
abstract: Nonsense-mediated mRNA decay (NMD) in mammalian cells depends on phosphorylation of Upf1, an RNA-dependent ATPase and 5'-to-3' helicase. Upf1 phosphorylation is mediated by Smg1, a phosphoinositol 3-kinase-related protein kinase. Here, we describe a human protein, which we call hSmg5/7a, that manifests similarity to Caenorhabditis elegans NMD factors CeSMG5 and CeSMG7, as well as two Drosophila melanogaster proteins that are also similar to the C. elegans NMD factors. Results indicate that hSmg5/7a functions in the dephosphorylation of Upf1. Furthermore, hSmg5/7a copurifies with Upf1, Upf2, Upf3X, Smg1, and the catalytic subunit of protein phosphatase 2A. We also demonstrate that Upf2, another factor involved in NMD, is a phosphoprotein. However, hSmg5/7a plays no role in the dephosphorylation of Upf2. These data indicate that hSmg5/7a targets protein phosphatase 2A to Upf1 but not Upf2. Results of Western blotting reveal that hSmg5/7a is mostly cytoplasmic in HEK293T cells.
authors.affiliation: Department of Biochemistry and Biophysics, School of Medicine and Dentistry, University of Rochester, New York 14642, USA.
authors.forename: Shang-Yi
authors.initials: SY
authors.lastname: Chiu
authors.forename: Guillaume
authors.initials: G
authors.lastname: Serin
authors.forename: Osamu
authors.initials: O
authors.lastname: Ohara
authors.forename: Lynne E
authors.initials: LE
authors.lastname: Maquat
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015153:Blotting, Western; D017173:Caenorhabditis elegans / Q000378:metabolism*; D029742:Caenorhabditis elegans Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D002460:Cell Line; D018076:DNA, Complementary; D015801:Helminth Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D006801:Humans; D052998:Microcystins; D008969:Molecular Sequence Data; D010456:Peptides, Cyclic / Q000737:chemistry; D010766:Phosphorylation; D020365:RNA Helicases / Q000302:isolation & purification / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D015534:Trans-Activators
chemical_list: D029742:Caenorhabditis elegans Proteins; D002352:Carrier Proteins; D018076:DNA, Complementary; D015801:Helminth Proteins; D052998:Microcystins; D010456:Peptides, Cyclic; C472410:SMG-5 protein, C elegans; C117551:SMG-7 protein, C elegans; D015534:Trans-Activators; C078588:microcystin; D020365:RNA Helicases; C101828:UPF1 protein, human