BLM helicase facilitates RNA polymerase I-mediated ribosomal RNA transcription

• Published in: Human molecular genetics Vol. 21; no. 5; pp. 1172 - 1183
• Main Authors: Grierson, Patrick M., Lillard, Kate, Behbehani, Gregory K., Combs, Kelly A., Bhattacharyya, Saumitri, Acharya, Samir, Groden, Joanna
• Format: Journal Article
• Language: English
• Published: Oxford Oxford University Press 01.03.2012
• Subjects: Biological and medical sciences; Cell Line; Cell Line, Tumor; Cell Nucleolus - metabolism; Cell Nucleus - metabolism; Dactinomycin - pharmacology; DNA - chemistry; DNA - metabolism; DNA, Ribosomal - chemistry; DNA, Ribosomal - metabolism; Fundamental and applied biological sciences. Psychology; Genetics of eukaryotes. Biological and molecular evolution; Humans; Molecular and cellular biology; Molecular genetics; Nucleic Acid Conformation; Protein Binding; Protein Subunits - metabolism; Recombinant Fusion Proteins - metabolism; RecQ Helicases - genetics; RecQ Helicases - metabolism; RNA Polymerase I - antagonists & inhibitors; RNA Polymerase I - metabolism; RNA, Ribosomal - genetics; Transcription, Genetic; Transcription. Transcription factor. Splicing. Rna processing; Genetics; Transcription; RNA polymerase I; Ribosomal RNA
• ISSN: 0964-6906; 1460-2083
• DOI: 10.1093/hmg/ddr545

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. 3H-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.