title: BLM helicase facilitates RNA polymerase I-mediated ribosomal RNA transcription.
abstract: Bloom's syndrome (BS) is an autosomal recessive disorder that is invariably characterized by severe growth retardation and cancer predisposition. The Bloom's syndrome helicase (BLM), mutations of which lead to BS, localizes to promyelocytic leukemia protein bodies and to the nucleolus of the cell, the site of RNA polymerase I-mediated ribosomal RNA (rRNA) transcription. rRNA transcription is fundamental for ribosome biogenesis and therefore protein synthesis, cellular growth and proliferation; its inhibition limits cellular growth and proliferation as well as bodily growth. We report that nucleolar BLM facilitates RNA polymerase I-mediated rRNA transcription. Immunofluorescence studies demonstrate the dependance of BLM nucleolar localization upon ongoing RNA polymerase I-mediated rRNA transcription. In vivo protein co-immunoprecipitation demonstrates that BLM interacts with RPA194, a subunit of RNA polymerase I. (3)H-uridine pulse-chase assays demonstrate that BLM expression is required for efficient rRNA transcription. In vitro helicase assays demonstrate that BLM unwinds GC-rich rDNA-like substrates that form in the nucleolus and normally inhibit progression of the RNA polymerase I transcription complex. These studies suggest that nucleolar BLM modulates rDNA structures in association with RNA polymerase I to facilitate RNA polymerase I-mediated rRNA transcription. Given the intricate relationship between rDNA metabolism and growth, our data may help in understanding the etiology of proportional dwarfism in BS.
authors: Department of Molecular Virology, Immunology and Medical Genetics, The Ohio State University College of Medicine, Columbus, OH 43210-2207, USA.
authors: Patrick M
authors: PM
authors: Grierson
authors: Kate
authors: K
authors: Lillard
authors: Gregory K
authors: GK
authors: Behbehani
authors: Kelly A
authors: KA
authors: Combs
authors: Saumitri
authors: S
authors: Bhattacharyya
authors: Samir
authors: S
authors: Acharya
authors: Joanna
authors: J
authors: Groden
mesh_terms: D002460:Cell Line; D045744:Cell Line, Tumor; D002466:Cell Nucleolus / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism; D004247:DNA / Q000737:chemistry / Q000378:metabolism; D004275:DNA, Ribosomal / Q000737:chemistry / Q000378:metabolism; D003609:Dactinomycin / Q000494:pharmacology; D006801:Humans; D009690:Nucleic Acid Conformation; D011485:Protein Binding; D021122:Protein Subunits / Q000378:metabolism; D012318:RNA Polymerase I / Q000037:antagonists & inhibitors / Q000378:metabolism*; D012335:RNA, Ribosomal / Q000235:genetics*; D053484:RecQ Helicases / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D004275:DNA, Ribosomal; D021122:Protein Subunits; D012335:RNA, Ribosomal; D011993:Recombinant Fusion Proteins; D003609:Dactinomycin; D004247:DNA; D012318:RNA Polymerase I; C097151:Bloom syndrome protein; D053484:RecQ Helicases