Abstract
The presence of actin and nuclear myosin I (NMI) in the nucleus suggests a role for these motor proteins in nuclear functions. We have investigated the role of actin and nuclear myosin I (NMI) in the transcription of ribosomal RNA genes (rDNA). Both proteins are associated with rDNA and are required for RNA polymerase I (Pol I) transcription. Microinjection of antibodies against actin or NMI, as well as short interfering RNA-mediated depletion of NMI, decreased Pol I transcription in vivo, whereas overexpression of NMI augmented pre-rRNA synthesis. In vitro, recombinant NMI activated Pol I transcription, and antibodies to NMI or actin inhibited Pol I transcription both on naked DNA and pre-assembled chromatin templates. Whereas actin associated with Pol I, NMI bound to Pol I through the transcription-initiation factor TIF-IA. The association with Pol I requires phosphorylation of TIF-IA at Ser 649 by RSK kinase, indicating a role for NMI in the growth-dependent regulation of rRNA synthesis.
Publication types
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, Non-P.H.S.
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Actins / metabolism*
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Antibodies / pharmacology
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Cell Line
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Cell Line, Tumor
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Cell Nucleus / genetics
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Cell Nucleus / metabolism*
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DNA, Ribosomal / genetics
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Humans
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Myosin Type I / metabolism*
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Pol1 Transcription Initiation Complex Proteins
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Protein Binding / genetics
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Protein Kinases / genetics
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Protein Kinases / metabolism
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RNA Interference
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RNA Polymerase I / biosynthesis*
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RNA Polymerase I / genetics
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RNA, Ribosomal / biosynthesis*
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RNA, Ribosomal / genetics
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Recombinant Fusion Proteins / genetics
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Recombinant Fusion Proteins / metabolism
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Ribosomal Protein S6 Kinases
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Serine / metabolism
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Transcription Factors / genetics
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Transcription Factors / metabolism
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Transcription, Genetic / genetics*
Substances
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Actins
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Antibodies
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DNA, Ribosomal
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Pol1 Transcription Initiation Complex Proteins
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RNA, Ribosomal
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RRN3 protein, human
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Recombinant Fusion Proteins
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Transcription Factors
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Serine
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Protein Kinases
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Ribosomal Protein S6 Kinases
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RNA Polymerase I
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Myosin Type I