To act as guides in the RNA interference (RNAi) pathway, small interfering RNAs (siRNAs) must be unwound into their component strands, then assembled with proteins to form the RNA-induced silencing complex (RISC), which catalyzes target messenger RNA cleavage. Thermodynamic differences in the base-pairing stabilities of the 5' ends of the two approximately 21-nucleotide siRNA strands determine which siRNA strand is assembled into the RISC. We show that in Drosophila, the orientation of the Dicer-2/R2D2 protein heterodimer on the siRNA duplex determines which siRNA strand associates with the core RISC protein Argonaute 2. R2D2 binds the siRNA end with the greatest double-stranded character, thereby orienting the heterodimer on the siRNA duplex. Strong R2D2 binding requires a 5'-phosphate on the siRNA strand that is excluded from the RISC. Thus, R2D2 is both a protein sensor for siRNA thermodynamic asymmetry and a licensing factor for entry of authentic siRNAs into the RNAi pathway.
"siR- NAs are 21-nt long duplex RNAs that are bound by a heterodimer between Dcr-2 and r2d2, a dsRBP partner . The Dcr-2/r2d2 complex transfers the duplex siRNA to Argonaute-2 (AGO2) to form siRNA programmed RISC (siRISC)  . Mature siRISC that carries only the guide strand of the siRNA duplex is formed after AGO2 cleaves the passenger strand that is then released and further degraded  . "
[Show abstract][Hide abstract] ABSTRACT: Viral RNA is a common activator of antiviral responses. In this review, we dissect the mechanism of viral RNA recognition by the small interfering RNA pathway in Drosophila melanogaster. This antiviral response in fruit flies can help understand general principles of nucleic acid recognition.
Microbes and Infection 09/2014; 16(12). DOI:10.1016/j.micinf.2014.09.001 · 2.86 Impact Factor
"With the help of a nuclear transport receptor (exportin-5) and Ran-GTP, pre-miRNAs are transported from nucleus to cytoplasm [22, 23]. In the cytoplasm, pre-miRNAs are recognized by Dicer, which works in cooperation with human immunodeficiency virus (HIV-1) transactivating response (TAR) RNA binding protein (TRBP or Loquacious in Drosophila) to cleave pre-miRNAs into miRNA duplexes [24–28]. Together with Argonaute and other proteins, a miRNA duplex is then loaded to generate RISC [29–31]. "
[Show abstract][Hide abstract] ABSTRACT: NF- κ B signaling network is a crucial component of innate immunity. miRNAs are a subtype of small noncoding RNAs, involved in regulation of gene expression at the posttranscriptional level. Increasing evidence has emerged that miRNAs play an important role in regulation of NF- κ B signaling pathway during viral infections. Both host and viral miRNAs are attributed to modulation of NF- κ B activity, thus affecting viral infection and clearance. Understandings of the mechanisms of these miRNAs will open a direction for development of novel antivirus drugs.
"Recent studies of the molecular mechanism that underly the specificity of the RNAi machinery indicate that the protein complex that mediate the recognition of the target RNA by the short dsRNA are not symmetrical. Thus, via mechanisms that are not fully understood, RISC treats only one of the strands as a guide (Tomari et al., 2004; Rand et al., 2005; Betancur and Tomari, 2012; Noland and Doudna, 2013). It is likely that a similar mechanism is at play here. "
[Show abstract][Hide abstract] ABSTRACT: Neurons regulate ionic fluxes across their plasma membrane to maintain their excitable properties under varying environmental conditions. However, the mechanisms that regulate ion channels abundance remain poorly understood. Here we show that pickpocket 29 (ppk29), a gene that encodes a Drosophila degenerin/epithelial sodium channel (DEG/ENaC), regulates neuronal excitability via a protein-independent mechanism. We demonstrate that the mRNA 3′UTR of ppk29 affects neuronal firing rates and associated heat-induced seizures by acting as a natural antisense transcript (NAT) that regulates the neuronal mRNA levels of seizure (sei), the Drosophila homolog of the human Ether-à-go-go Related Gene (hERG) potassium channel. We find that the regulatory impact of ppk29 mRNA on sei is independent of the sodium channel it encodes. Thus, our studies reveal a novel mRNA dependent mechanism for the regulation of neuronal excitability that is independent of protein-coding capacity. DOI: http://dx.doi.org/10.7554/eLife.01849.001
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.