title: Regulated compartmentalization of the putative DEAD-box helicase MDDX28 within the mitochondria in COS-1 cells.
abstract: We recently cloned a putative DEAD-box helicase MDDX28 and found that it was localized to the nuclei and mitochondria of COS-1 cells. The mitochondrial localization of MDDX28 is largely diffuse. We have, however, used immunofluorescence and immunogold cytochemistry to show that the MDDX28 protein is localized in a distinct mitochondrial subcompartment in 5-10% of COS-1 cells. This proportion increases to approximately 35% after treatment with ethidium bromide, suggesting upregulation following transcription inhibition. To our knowledge, this is the first example of protein relocation in the mitochondria caused by transcription inhibition. The mitochondrial subcompartmentation of MDDX28 was negatively affected by mutations in a RNA-binding domain and three basic domains previously shown to be important in transcription-dependent intranuclear localization. Furthermore, immunogold cytochemistry and fractionation of rat liver indicated that the protein is a part of an RNA-protein (RNP) complex interacting peripherally with the mitochondrial inner membrane. Our results reveal new principles for regulation of protein localization in the mitochondria and suggest parallels between the function of the MDDX28 protein in the nucleus and mitochondria.
authors.affiliation: Biotechnology Centre of Oslo, University of Oslo, N0349 Oslo, Norway.
authors.forename: Rut
authors.initials: R
authors.lastname: Valgardsdottir
authors.forename: Ole Petter
authors.initials: OP
authors.lastname: Ottersen
authors.forename: Hans
authors.initials: H
authors.lastname: Prydz
mesh_terms: D000818:Animals; D019556:COS Cells; D002451:Cell Compartmentation; D002467:Cell Nucleus / Q000201:enzymology*; D002522:Chlorocebus aethiops; D053487:DEAD-box RNA Helicases; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004996:Ethidium / Q000494:pharmacology; D006801:Humans; D007150:Immunohistochemistry; D008099:Liver / Q000187:drug effects / Q000201:enzymology; D008930:Mitochondria, Liver / Q000201:enzymology*; D009154:Mutation; D012313:RNA / Q000378:metabolism; D020365:RNA Helicases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D051381:Rats; D014158:Transcription, Genetic / Q000187:drug effects / Q000502:physiology
chemical_list: D004791:Enzyme Inhibitors; D012313:RNA; C434959:DDX28 protein, human; D053487:DEAD-box RNA Helicases; D020365:RNA Helicases; D004996:Ethidium