Nucleolar localization of murine nuclear DNA helicase II (RNA helicase A).
Nuclear DNA helicase II (NDH II) is a highly conserved member of the DEXH superfamily of eukaryotic helicases, whose physiological role is still unclear. To explore the function of NDH II, we studied the intracellular distribution of NDH II of different mammalian species by immunofluorescence and compared these findings with the known role of the Drosophila homologue MLE that is involved in sex-specific gene dosage compensation. NDH II displayed an apparent nucleolar localization in murine cells, whereas in cells from all other mammalian species examined so far the protein was confined to the nucleoplasm and apparently excluded from the nucleoli. The nucleolar localization of mouse NDH II strongly suggests a role in ribosomal RNA biosynthesis. Immunoelectron microscopic studies revealed that the mouse NDH II was found at the dense fibrillar components of the nucleoli, and a significant percentage of NDH II molecules colocalized with the RNA polymerase I (Pol I) transcription factor UBF (upstream binding factor). Additionally, the nucleolar localization of NDH II coincided with a preferential immunolabeling pattern of nascent transcripts with bromouridine (BrUMP). Furthermore, mouse NDH II redistributed in mitosis in a manner highly correlated with Pol I activity. Conditions leading to the inhibition of Pol I activity in the interphase decreased the amount of NDH II in the nucleoli that diffused into the nucleoplasm and the cytosol. Contrary to the effect of inhibiting rRNA synthesis, treatment of mouse cells with the translation inhibitor cycloheximide did not compromise the nucleolar localization of murine NDH II.
Department of Biochemistry and Department of Electron Microscopy and Molecular Cytology, Institute for Molecular Biotechnology, Beutenbergstrasse 11, D-07745 Jena, Germany.
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Grosse
D016475:3T3 Cells; D017766:Acid Anhydride Hydrolases / Q000032:analysis / Q000235:genetics; D000251:Adenosine Triphosphatases / Q000032:analysis / Q000235:genetics*; D000818:Animals; D002466:Cell Nucleolus / Q000201:enzymology* / Q000235:genetics / Q000648:ultrastructure; D003513:Cycloheximide / Q000494:pharmacology; D053487:DEAD-box RNA Helicases; D004265:DNA Helicases / Q000032:analysis / Q000235:genetics*; D005455:Fluorescent Antibody Technique; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects / Q000502:physiology; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D016253:Microscopy, Immunoelectron; D008938:Mitosis / Q000502:physiology; D008969:Molecular Sequence Data; D043583:Nucleoside-Triphosphatase; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D020365:RNA Helicases / Q000032:analysis / Q000235:genetics; D012335:RNA, Ribosomal / Q000096:biosynthesis / Q000235:genetics; D011817:Rabbits; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic / Q000187:drug effects / Q000502:physiology; D014544:Uridine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology
C506727:Dhx9 protein, mouse; D011500:Protein Synthesis Inhibitors; D012335:RNA, Ribosomal; C018009:5-bromouridine triphosphate; D003513:Cycloheximide; D017766:Acid Anhydride Hydrolases; D000251:Adenosine Triphosphatases; D043583:Nucleoside-Triphosphatase; D004265:DNA Helicases; D053487:DEAD-box RNA Helicases; D020365:RNA Helicases; D014544:Uridine Triphosphate