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      Incorporation of pseudouridine into mRNA enhances translation by diminishing PKR activation

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          Abstract

          Previous studies have shown that the translation level of in vitro transcribed messenger RNA (mRNA) is enhanced when its uridines are replaced with pseudouridines; however, the reason for this enhancement has not been identified. Here, we demonstrate that in vitro transcripts containing uridine activate RNA-dependent protein kinase (PKR), which then phosphorylates translation initiation factor 2-alpha (eIF-2α), and inhibits translation. In contrast, in vitro transcribed mRNAs containing pseudouridine activate PKR to a lesser degree, and translation of pseudouridine-containing mRNAs is not repressed. RNA pull-down assays demonstrate that mRNA containing uridine is bound by PKR more efficiently than mRNA with pseudouridine. Finally, the role of PKR is validated by showing that pseudouridine- and uridine-containing RNAs were translated equally in PKR knockout cells. These results indicate that the enhanced translation of mRNAs containing pseudouridine, compared to those containing uridine, is mediated by decreased activation of PKR.

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          Most cited references49

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          Pseudouridine in RNA: what, where, how, and why.

          Pseudouridine (5-ribosyluracil) is a ubiquitous yet enigmatic constituent of structural RNAs (transfer, ribosomal, small nuclear, and small nucleolar). Although pseudouridine (psi) was the first modified nucleoside to be discovered in RNA, and is the most abundant, its biosynthesis and biological roles have remained poorly understood since its identification as a "fifth nucleoside" in RNA. Recently, a combination of biochemical, biophysical, and genetic approaches has helped to illuminate the structural consequences of psi in polyribonucleotides, the biochemical mechanism of U-->psi isomerization in RNA, and the role of modification enzymes (psi synthases) and box H/ACA snoRNAs, a class of eukaryotic small nucleolar RNAs, in the site-specific biosynthesis of psi. Through its unique ability to coordinate a structural water molecule via its free N1-H, psi exerts a subtle but significant "rigidifying" influence on the nearby sugar-phosphate backbone and also enhances base stacking. These effects may underlie the biological role of most (but perhaps not all) of the psi residues in RNA. Certain genetic mutants lacking specific psi residues in tRNA or rRNA exhibit difficulties in translation, display slow growth rates, and fail to compete effectively with wild-type strains in mixed culture. In particular, normal growth is severely compromised in an Escherichia coli mutant deficient in a pseudouridine synthase responsible for the formation of three closely spaced psi residues in the mRNA decoding region of the 23S rRNA. Such studies demonstrate that pseudouridylation of RNA confers an important selective advantage in a natural biological context.
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            2'-O-methyl-modified RNAs act as TLR7 antagonists.

            RNA molecules such as single-stranded RNA (ssRNA) and small interfering RNA (siRNA) duplexes induce Toll-like receptor (TLR)-mediated immune stimulation after intracellular delivery. We have previously shown that selective incorporation of 2'-O-methyl (2'OMe) residues into siRNA abrogates cytokine production without reduction of gene silencing activity. Here we show that 2'OMe-modified RNA acts as a potent inhibitor of RNA-mediated cytokine induction in both human and murine systems. This activity does not require the direct incorporation of 2'OMe nucleotides into the immunostimulatory RNA or that the 2'OMe nucleotide-containing RNA be annealed as a complementary strand to form a duplex. Our results indicate that 2'OMe RNA acts as a potent antagonist of immunostimulatory RNA. We further show that 2'OMe RNA is able significantly to reduce both interferon-alpha (IFN-alpha) and interleukin-6 (IL-6) induction by the small-molecule TLR7 agonist loxoribine in human peripheral blood mononuclear cells (human PBMCs), in murine Flt3L dendritic cells (Flt3L DCs), and in vivo in mice. These results indicate that 2'OMe-modified RNA may have utility as an inhibitor of TLR7 with potential applications in the treatment of inflammatory and autoimmune diseases that involve TLR7-mediated immune stimulation.
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              Molecular basis of double-stranded RNA-protein interactions: structure of a dsRNA-binding domain complexed with dsRNA.

              Protein interactions with double-stranded RNA (dsRNA) are critical for many cell processes; however, in contrast to protein-dsDNA interactions, surprisingly little is known about the molecular basis of protein-dsRNA interactions. A large and diverse class of proteins that bind dsRNA do so by utilizing an approximately 70 amino acid motif referred to as the dsRNA-binding domain (dsRBD). We have determined a 1.9 A resolution crystal structure of the second dsRBD of Xenopus laevis RNA-binding protein A complexed with dsRNA. The structure shows that the protein spans 16 bp of dsRNA, interacting with two successive minor grooves and across the intervening major groove on one face of a primarily A-form RNA helix. The nature of these interactions explains dsRBD specificity for dsRNA (over ssRNA or dsDNA) and the apparent lack of sequence specificity. Interestingly, the dsRBD fold resembles a portion of the conserved core structure of a family of polynucleotidyl transferases that includes RuvC, MuA transposase, retroviral integrase and RNase H. Structural comparisons of the dsRBD-dsRNA complex and models proposed for polynucleotidyl transferase-nucleic acid complexes suggest that similarities in nucleic acid binding also exist between these families of proteins.
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                Author and article information

                Journal
                Nucleic Acids Res
                nar
                nar
                Nucleic Acids Research
                Oxford University Press
                0305-1048
                1362-4962
                September 2010
                September 2010
                10 May 2010
                10 May 2010
                : 38
                : 17
                : 5884-5892
                Affiliations
                1Department of Medicine, 2Department of Neurosurgery, University of Pennsylvania, Philadelphia, PA, 3Department of Chemistry, Pennsylvania State University, University Park, PA and 4Department of Neurology, University of Pennsylvania, Philadelphia, PA, USA
                Author notes
                *To whom correspondence should be addressed. Tel: +1 215 662 7927; Fax: +1 215 349 8157; Email: kariko@ 123456mail.med.upenn.edu
                Article
                gkq347
                10.1093/nar/gkq347
                2943593
                20457754
                b9123cdb-987f-4af1-a1f2-c75f45310038
                © The Author(s) 2010. Published by Oxford University Press.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( http://creativecommons.org/licenses/by-nc/2.5), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 8 February 2010
                : 8 April 2010
                : 20 April 2010
                Categories
                RNA

                Genetics
                Genetics

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