Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.7.6 (RNA polymerase)
 34,946 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A nuclear isoform of myosin I beta that contains a unique 16-amino acid amino-terminal extension has been identified. An affinity-purified antibody to the 16-amino acid peptide demonstrated nuclear staining. Confocal and electron microscopy revealed that nuclear myosin I beta colocalized with RNA polymerase II in an alpha-amanitin- and actinomycin D-sensitive manner. The antibody coimmunoprecipitated RNA polymerase II and blocked in vitro RNA synthesis. This isoform of myosin I beta appears to be in a complex with RNA polymerase II and may affect transcription.
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PMID:A myosin I isoform in the nucleus. 1103 Jun 52

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.
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PMID:Nuclear actin and myosin I are required for RNA polymerase I transcription. 1555 34

Actin is associated with all three nuclear RNA polymerases and acts in concert with nuclear myosin I (NM1) to drive transcription. Practically nothing is known regarding the state of actin and the functional interplay of actin and NM1 in transcription. Here we show that actin and NM1 act in concert to promote RNA polymerase I (Pol I) transcription. Drugs that prevent actin polymerization or inhibit myosin function inhibit Pol I transcription in vivo and in vitro. Mutants that stabilize the polymeric state actin are tightly associated with Pol I and activate transcription, whereas a polymerization-deficient mutant does not bind to Pol I and does not promote rDNA transcription. Consistent with nuclear actin and myosin synergizing in transcription activation, NM1 mutants that lack specific functions, such as binding to ATP, actin, or calmodulin, are incapable of associating with Pol I and rDNA. The results show that actin polymerization and the motor function of NM1 are required for association with the Pol I transcription machinery and transcription activation. These observations provide insights into the cooperative action of actin and myosin in the nucleus and reveal an actomyosin-based mechanism in transcription.
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PMID:Nuclear myosin I acts in concert with polymeric actin to drive RNA polymerase I transcription. 1823 Jul

Nuclear actin and nuclear myosin I (NMI) are important players in transcription of ribosomal genes. Transcription of rDNA takes place in highly organized intranuclear compartment, the nucleolus. In this study, we characterized the localization of these two proteins within the nucleolus of HeLa cells with high structural resolution by means of electron microscopy and gold-immunolabeling. We demonstrate that both actin and NMI are localized in specific compartments within the nucleolus, and the distribution of NMI is transcription-dependent. Moreover, a pool of NMI is present in the foci containing nascent rRNA transcripts. Actin, in turn, is present both in transcriptionally active and inactive regions of the nucleolus and colocalizes with RNA polymerase I and UBF. Our data support the involvement of actin and NMI in rDNA transcription and point out to other functions of these proteins in the nucleolus, such as rRNA maturation and maintenance of nucleolar architecture.
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PMID:Transcription-dependent rearrangements of actin and nuclear myosin I in the nucleolus. 2068 8

In vertebrates, two myosin Ic isoforms that localize to the cytoplasm and to the nucleus have been characterized. The isoform that predominantly localizes to the nucleus is called nuclear myosin I (NMI). NMI has been identified as a key factor involved in nuclear processes such as transcription by RNA polymerases I and II and intranuclear transport processes. We report here the identification of a previously uncharacterized third MYOIC gene product that is called isoform A. Similar to NMI, this isoform contains a unique N-terminal peptide sequence, localizes to the nucleus and colocalizes with RNA polymerase II. However, unlike NMI, upon exposure to inhibitors of RNA polymerase II transcription the newly identified isoform translocates to nuclear speckles. Furthermore, in contrast to NMI, this new isoform is absent from nucleoli and does not colocalize with RNA polymerase I. Our results suggest an unexpected diversity among nuclear myosin Ic isoforms in respect to their intranuclear localization and interaction with nuclear binding partners that could provide new insights into the regulation of myosin-dependent nuclear processes.
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PMID:Identification and characterization of a novel myosin Ic isoform that localizes to the nucleus. 2273 83