Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.7.7.6 (RNA polymerase)
34,946 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

microRNAs (miRNAs) are generated from long primary (pri-) RNA polymerase II (Pol II)-derived transcripts by two RNase III processing reactions: Drosha cleavage of nuclear pri-miRNAs and Dicer cleavage of cytoplasmic pre-miRNAs. Here we show that Drosha cleavage occurs during transcription acting on both independently transcribed and intron-encoded miRNAs. We also show that both 5'-3' and 3'-5' exonucleases associate with the sites where co-transcriptional Drosha cleavage occurs, promoting intron degradation before splicing. We finally demonstrate that miRNAs can also derive from 3' flanking transcripts of Pol II genes. Our results demonstrate that multiple miRNA-containing transcripts are co-transcriptionally cleaved during their synthesis and suggest that exonucleolytic degradation from Drosha cleavage sites in pre-mRNAs may influence the splicing and maturation of numerous mRNAs.
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PMID:Primary microRNA transcripts are processed co-transcriptionally. 1917 42

RNA-directed DNA methylation (RdDM) is a nuclear process in which small interfering RNAs (siRNAs) direct the cytosine methylation of DNA sequences that are complementary to the siRNAs. In plants, double stranded-RNAs (dsRNAs) generated by RNA-dependent RNA polymerase 2 (RDR2) serve as precursors for Dicer-like 3 dependent biogenesis of 24-nt siRNAs. Plant specific RNA polymerase IV (Pol IV) is presumed to generate the initial RNA transcripts that are substrates for RDR2. siRNAs are loaded onto an argonaute4-containing RISC (RNA-induced silencing complex) that targets the de novo DNA methyltransferase DRM2 to RdDM target loci. Nascent RNA transcripts from the target loci are generated by another plant-specific RNA polymerase, Pol V, and these transcripts help recruit complementary siRNAs and the associated RdDM effector complex to the target loci in a transcription-coupled DNA methylation process. Small RNA binding proteins such as ROS3 may direct target-specific DNA demethylation by the ROS1 family of DNA demethylases. Chromatin remodeling enzymes and histone modifying enzymes also participate in DNA methylation and possibly demethylation. One of the well studied functions of RdDM is transposon silencing and genome stability. In addition, RdDM is important for paramutation, imprinting, gene regulation, and plant development. Locus-specific DNA methylation and demethylation, and transposon activation under abiotic stresses suggest that RdDM is also important in stress responses of plants. Further studies will help illuminate the functions of RdDM in the dynamic control of epigenomes during development and environmental stress responses.
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PMID:RNA-directed DNA methylation and demethylation in plants. 1938 59

Human Adenovirus type 5 encodes two short RNA polymerase III transcripts, the virus-associated (VA) RNAI and VA RNAII, which can adopt stable hairpin structures that resemble micro-RNA precursors. The terminal stems of the VA RNAs are processed into small RNAs (mivaRNAs) that are incorporated into RISC. It has been reported that VA RNAI has two transcription initiation sites, which produce two VA RNAI species; a major species, VA RNAI(G), which accounts for 75% of the VA RNAI pool, and a minor species, VA RNAI(A), which initiates transcription three nucleotides upstream compared to VA RNAI(G). We show that this 5'-heterogeneity results in a dramatic difference in RISC assembly. Thus, both VA RNAI(G) and VA RNAI(A) are processed by Dicer at the same position in the terminal stem generating the same 3'-strand mivaRNA. This mivaRNA is incorporated into RISC with 200-fold higher efficiency compared to the 5'-strand of mivaRNAI. Of the small number of 5'-strands used in RISC assembly only VA RNAI(A) generated active RISC complexes. We also show that the 3'-strand of mivaRNAI, although being the preferred substrate for RISC assembly, generates unstable RISC complexes with a low in vitro cleavage activity, only around 2% compared to RISC assembled on the VA RNAI(A) 5'-strand.
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PMID:The 5'-end heterogeneity of adenovirus virus-associated RNAI contributes to the asymmetric guide strand incorporation into the RNA-induced silencing complex. 1975

Here, we show that recombinant Drosophila elp1 (D-elp1) produced in Sf9 cells or Escherichia coli, corresponding to the largest of the three subunits in the RNA polymerase II core elongator complex, has RNA-dependent RNA polymerase (RdRP) activity. D-elp1 is a noncanonical RdRP that can synthesize dsRNA from different ssRNA templates using either a primer-dependent or primer-independent initiation mechanism. Of the three core subunits, only D-elp1 depletion inhibits RNAi in S2 cells but does not affect micro RNA function. Furthermore, D-elp1 depletion results in increased steady state levels of representative transposon RNAs and a decrease in the corresponding transposon antisense transcripts and endo siRNAs. In contrast, although Dcr-2 depletion results in increased transposon RNA levels and a reduction in the corresponding endo siRNAs, there is no change in the transposon antisense RNA levels. In D-elp1 null third instar larvae transposon RNA levels are also increased and the corresponding transposon antisense RNAs are reduced. D-elp1 associates tightly with Dcr-2, similar to the Dicer-RdRP interaction observed in lower eukaryotes. These results identify an aspect of the RNAi pathway in Drosophila that suggest transposon derived endo siRNAs, critical for transposon suppression, are produced, in part, in a D-elp1 dependent step that converts transposon RNA into dsRNA that is subsequently processed by Dcr-2. The generality of this mechanism in genome defense and RNA silencing in higher eukaryotes is suggested.
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PMID:Identification of an RNA-dependent RNA polymerase in Drosophila involved in RNAi and transposon suppression. 2182 90

In lower eukaryotes, such as A. thaliana, C. elegans, S. pombe and N. crassa, RNA-dependent RNA polymerase (RdRP) is a required component of the RNA silencing pathway. Remarkably, even though robust RNA silencing occurs in Drosophila in response to exogenous dsRNA and siRNAs, no RdRP homolog has been identified in the Drosophila genome or in any other higher eukaryote characteristic of the known cellular RdRPs. We showed recently that the largest subunit of the Drosophila RNA polymerase II core elongator complex, called D-elp1, has RdRP activity capable of using unprimed or primed synthesis mechanisms to convert single stranded RNA templates into double stranded RNA (dsRNA) that can be cleaved by Dcr-2. Loss of D-elp1 inhibits both siRNA and dsRNA directed RNAi in S2 cells but does not affect micro RNA targeting. Transposon RNA levels also increase with the loss of D-elp1 while the corresponding endo siRNAs, critical for transposon suppression, are dramatically reduced and this is correlated with a reduction in transposon antisense RNA levels. D-elp1 associates tightly with Dicer-2, similar to the Dicer-RdRP interaction observed in lower eukaryotes. With the exception of S. cerevisiae, which lacks the RNAi machinery altogether, RdRP activity is conserved in the elp1 homologs from S. pombe to human. This commentary focuses on the importance and universality of RdRP in RNA silencing.
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PMID:Identification of an RNA-dependent RNA polymerase in Drosophila establishes a common theme in RNA silencing. 2002 2

Canonical primary microRNA (pri-miRNA) precursors are transcribed by RNA polymerase II and then processed by the Drosha endonuclease to generate approximately 60 nt pre-miRNA hairpins. Pre-miRNAs in turn are cleaved by Dicer to generate mature miRNAs. Previously, some short introns, called miRtrons, were reported to fold into pre-miRNA hairpins after splicing and debranching, and miRNAs can also be excised by Dicer cleavage of rare endogenous short hairpin RNAs. Here we report that the miRNAs encoded by murine gamma-herpesvirus 68 (MHV68) are also generated via atypical mechanisms. Specifically, MHV68 miRNAs are transcribed from RNA polymerase III promoters located within adjacent viral tRNA-like sequences. The resultant pri-miRNAs, which bear a 5' tRNA moiety, are not processed by Drosha but instead by cellular tRNase Z, which cleaves 3' to the tRNA to liberate pre-miRNA hairpins that are then processed by Dicer to yield the mature viral miRNAs.
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PMID:A mammalian herpesvirus uses noncanonical expression and processing mechanisms to generate viral MicroRNAs. 2012 62

Competition between mammalian RNAi-related gene silencing pathways is well documented. It is therefore important to identify all classes of small RNAs to determine their relationship with RNAi and how they affect each other functionally. Here, we identify two types of 5'-phosphate, 3'-hydroxylated human tRNA-derived small RNAs (tsRNAs). tsRNAs differ from microRNAs in being essentially restricted to the cytoplasm and in associating with Argonaute proteins, but not MOV10. The first type belongs to a previously predicted Dicer-dependent class of small RNAs that we find can modestly down-regulate target genes in trans. The 5' end of type II tsRNA was generated by RNaseZ cleavage downstream from a tRNA gene, while the 3' end resulted from transcription termination by RNA polymerase III. Consistent with their preferential association with the nonslicing Argonautes 3 and 4, canonical gene silencing activity was not observed for type II tsRNAs. The addition, however, of an oligonucleotide that was sense to the reporter gene, but antisense to an overexpressed version of the type II tsRNA, triggered robust, >80% gene silencing. This correlated with the redirection of the thus reconstituted fully duplexed double-stranded RNA into Argonaute 2, whereas Argonautes 3 and 4 were skewed toward less structured small RNAs, particularly single-strand RNAs. We observed that the modulation of tsRNA levels had minor effects on the abundance of microRNAs, but more pronounced changes in the silencing activities of both microRNAs and siRNAs. These findings support that tsRNAs are involved in the global control of small RNA silencing through differential Argonaute association, suggesting that small RNA-mediated gene regulation may be even more finely regulated than previously realized.
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PMID:Human tRNA-derived small RNAs in the global regulation of RNA silencing. 2018 38

RNA interference (RNAi) is an evolutionarily conserved process that silences gene expression through double-stranded RNA species in a sequence-specific manner. Small interfering RNAs (siRNAs) can promote sequence-specific degradation and/or translational repression of target RNA by activation of the RNA-induced silencing complex (RISC). Traditionally, silencing in mammalian cells had been achieved by transfection of synthetically derived siRNA duplexes, resulting in transient gene suppression of the target sequence. As the technology was advanced, inhibitory short-hairpin-shaped RNAs (shRNAs) could be produced by transcription from RNA polymerase-III (pol-III)-driven promoters, such as H1, U6, or cytomegalovirus (CMV)-enhanced pol III promoters. Following transcription, the shRNAs are processed by the enzyme Dicer into active siRNA. This approach allows for the continuous production of siRNA within cells using a DNA template and offers increased options for delivery of the pol-III-driven transcriptional units. A number of different viral vectors, as well as plasmid DNAs, have been utilized to deliver shRNA to mammalian cells. Here, the Tc1/mariner DNA transposon Sleeping Beauty (SB) is used as a tool to deliver shRNA-encoding transcriptional units. The SB transposon system uses a "cut-and-paste" mechanism to insert the transposon into random TA dinucleotides within the target genome. The shRNAs are then processed and used for gene knockdown.
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PMID:Delivery of small interfering RNA (siRNA) using the sleeping beauty transposon. 2104 94

Quantitative real-time PCR (QPCR) has emerged as an accurate and valuable tool in profiling gene expression levels. One of its many advantages is a lower detection limit compared to other methods of gene expression profiling while using smaller amounts of input for each assay. Automated qPCR setup has improved this field by allowing for greater reproducibility. Its convenient and rapid setup allows for high-throughput experiments, enabling the profiling of many different genes simultaneously in each experiment. This method along with internal plate controls also reduces experimental variables common to other techniques. We recently developed a qPCR assay for profiling of pre-microRNAs (pre-miRNAs) using a set of 186 primer pairs. MicroRNAs have emerged as a novel class of small, non-coding RNAs with the ability to regulate many mRNA targets at the post-transcriptional level. These small RNAs are first transcribed by RNA polymerase II as a primary miRNA (pri-miRNA) transcript, which is then cleaved into the precursor miRNA (pre-miRNA). Pre-miRNAs are exported to the cytoplasm where Dicer cleaves the hairpin loop to yield mature miRNAs. Increases in miRNA levels can be observed at both the precursor and mature miRNA levels and profiling of both of these forms can be useful. There are several commercially available assays for mature miRNAs; however, their high cost may deter researchers from this profiling technique. Here, we discuss a cost-effective, reliable, SYBR-based qPCR method of profiling pre-miRNAs. Changes in pre-miRNA levels often reflect mature miRNA changes and can be a useful indicator of mature miRNA expression. However, simultaneous profiling of both pre-miRNAs and mature miRNAs may be optimal as they can contribute nonredundant information and provide insight into microRNA processing. Furthermore, the technique described here can be expanded to encompass the profiling of other library sets for specific pathways or pathogens.
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PMID:Profiling of pre-micro RNAs and microRNAs using quantitative real-time PCR (qPCR) arrays. 2117 61

General transcription factor IIH (TFIIH) is a complex RNA polymerase II basal transcription factor comprising 10 different polypeptides that display activities involved in transcription and DNA repair processes. Although biochemical studies have uncovered TFIIH importance, little is known about how the mRNAs that code for TFIIH subunits are regulated. Here it is shown that mRNAs encoding seven of the TFIIH subunits (p34, p44, p52, p62, XPB, CDK7, and p8) are regulated at the posttranscriptional level in a Dicer-dependent manner. Indeed, abolition of the miRNA pathway induces abnormal accumulation, stabilization, and translational activation of these seven mRNAs. Herein, miR-27a was identified as a key regulator of p44 mRNA. Moreover, miR-27a was shown to destabilize the p44 subunit of the TFIIH complex during the G2-M phase, thereby modulating the transcriptional shutdown observed during this transition. This work is unique in providing a demonstration of global transcriptional regulation through the action of a single miRNA.
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PMID:MicroRNA-27a regulates basal transcription by targeting the p44 subunit of general transcription factor IIH. 2155 43


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