title: Identification of a cytoplasmic complex that adds a cap onto 5'-monophosphate RNA.
abstract: Endonuclease decay of nonsense-containing beta-globin mRNA in erythroid cells generates 5'-truncated products that were reported previously to have a cap or caplike structure. We confirmed that this 5' modification is indistinguishable from the cap on full-length mRNA, and Western blotting, immunoprecipitation, and active-site labeling identified a population of capping enzymes in the cytoplasm of erythroid and nonerythroid cells. Cytoplasmic capping enzyme sediments in a 140-kDa complex that contains a kinase which, together with capping enzyme, converts 5'-monophosphate RNA into 5'-GpppX RNA. Capping enzyme shows diffuse and punctate staining throughout the cytoplasm, and its staining does not overlap with P bodies or stress granules. Expression of inactive capping enzyme in a form that is restricted to the cytoplasm reduced the ability of cells to recover from oxidative stress, thus supporting a role for capping in the cytoplasm and suggesting that some mRNAs may be stored in an uncapped state.
authors.affiliation: Department of Molecular and Cellular Biochemistry, the Ohio State University, Columbus, OH 43210-1218, USA.
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Otsuka
authors.forename: Nancy L
authors.initials: NL
authors.lastname: Kedersha
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Schoenberg
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D003593:Cytoplasm / Q000201:enzymology*; D041905:Erythroid Cells; D006801:Humans; D051379:Mice; D009097:Multienzyme Complexes / Q000032:analysis*; D009708:Nucleotidases; D009713:Nucleotidyltransferases; D018384:Oxidative Stress; D012315:RNA Caps; D012333:RNA, Messenger / Q000378:metabolism*; D014162:Transfection; D055544:beta-Globins / Q000235:genetics
chemical_list: D009097:Multienzyme Complexes; D012315:RNA Caps; D012333:RNA, Messenger; D055544:beta-Globins; D009713:Nucleotidyltransferases; D009708:Nucleotidases; C510372:Rngtt protein, mouse