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PubMed1997

Role of double-stranded RNA-activated protein kinase in human hematological malignancies.

The double-stranded RNA (dsRNA)-activated protein kinase (PKR) is one of many genes induced by IFN. The PKR sequentially undergoes autophosphorylation and activation on binding to dsRNA. Previous studies have shown that PKR may be an important factor in the regulation of viral and cellular protein synthesis. Recent studies suggest that PKR may function as a tumor suppressor gene. The role of PKR in various human leukemic cells was therefore investigated. PKR mRNA levels by reverse transcription-PCR, protein expression by Western blot and FACScan analysis, and activity by phosphorylation status were studied. The expression of a known inhibitor of PKR, p58, was also investigated at mRNA and protein levels. A total of 24 samples from normal mononuclear cells (MNCs), 26 samples of acute lymphoblastic leukemia, 26 samples of acute myelogenous leukemia, 32 samples of chronic lymphocytic leukemia, and 5 samples of hairy cell leukemia was investigated. Mean mRNA levels were increased in acute lymphoblastic leukemia and acute myelogenous leukemia and decreased in chronic lymphocytic leukemia compared to normal MNCs. The mRNA levels in hairy cell leukemia were similar to those of normal MNCs. PKR protein was detectable in normal MNCs and leukemic cell extracts, and on FACScan analysis, more than 70% of cells stained positive for PKR. PKR activity was detectable in all samples investigated and was enhanced 4-23-fold in the presence of the synthetic dsRNA, poly(I) x poly(C). Protein expression of a known PKR inhibitor, p58, was barely detectable in normal MNCs and leukemic cells, with high expression in the HeLa cell line. These findings provide no evidence to support the hypothesis that PKR acts as a tumor suppressor in human leukemic cells.

Gene Expression Regulation, Enzymologic↗
PubMed1992

Immunohistochemical detection of double-stranded-RNA-dependent protein kinase (p68) with a novel monoclonal antibody TJ4C4. A case report of an AIDS-associated Kaposi's sarcoma treated with alpha-interferon.

Double-stranded RNA (dsRNA)-dependent protein kinase (p68) has been shown to be induced by alpha-interferon (IFN-alpha) in mammalian cells. It binds to dsRNA, and is believed to be a factor in the control of both cellular and viral protein synthesis. This report describes the use of a new monoclonal antibody (MAb) TJ4C4, to monitor levels of p68 in a patient with AIDS-associated Kaposi's sarcoma. Using a novel immunoperoxidase/iron staining method, we examined formalin-fixed, paraffin-embedded biopsies prior to, and 4 months after the initiation of IFN therapy. Immunostaining showed low levels (1+ staining) of p68 in the pretreatment tissue, whereas a marked increase (4+ staining) was noted during interferon treatment. This staining suggests an increased level of intracellular p68 expression. This patient has subsequently remained on IFN-alpha therapy and is alive with no evidence of Kaposi's sarcoma, 6 1/2 years after diagnosis. The use of MAb TJ4C4 will greatly facilitate the study of p68 kinase in clinical tissues, and may provide a way to monitor the effects of IFN therapy.

AIDS-Related Opportunistic Infections↗
PubMed1989

Purification and activation of the double-stranded RNA-dependent eIF-2 kinase DAI.

The double-stranded RNA (dsRNA)-dependent protein kinase DAI (also termed dsI and P1) possesses two kinase activities; one is an autophosphorylation activity, and the other phosphorylates initiation factor eIF-2. We purified the enzyme, in a latent form, to near homogeneity from interferon-treated human 293 cells. The purified enzyme consisted of a single polypeptide subunit of approximately 70,000 daltons, retained its dependence on dsRNA for activation, and was sensitive to inhibition by adenovirus VA RNAI. Autophosphorylation required a suitable concentration of dsRNA and was second order with respect to DAI concentration, which suggests an intermolecular mechanism in which one DAI molecule phosphorylates a neighboring molecule. Once autophosphorylated, the enzyme could phosphorylate eIF-2 but seemed unable to phosphorylate other DAI molecules, which implies a change in substrate specificity upon activation. VA RNAI blocked autophosphorylation and activation but permitted the activated enzyme to phosphorylate eIF-2. VA RNAI also blocked the binding of dsRNA to the enzyme. The data are consistent with a model in which activation requires the interaction of two molecules of DAI with dsRNA, followed by intermolecular autophosphorylation of the latent enzyme. VA RNAI would block activation by preventing the interaction between DAI and dsRNA.

Binding Sites↗
PubMed1995

Involvement of the double-stranded-RNA-dependent kinase PKR in interferon expression and interferon-mediated antiviral activity.

The signaling mechanisms responsible for the induced expression of interferon (IFN) genes by viral infection or double-stranded RNA (dsRNA) are not well understood. Here we investigate the role of the interferon-induced dsRNA-dependent protein kinase PKR in the regulation of IFN induction. Biological activities attributed to PKR include regulating protein synthesis, mediating IFN actions, and functioning as a possible tumor suppressor. Since binding of dsRNA is required for its activation, PKR has been considered as a candidate signal transducer for regulating IFN expression. To examine this role of PKR, loss-of-function phenotypes in stable transformants of promonocytic U-937 cells were achieved by two different strategies, overexpression of an antisense PKR transcript or a dominant negative PKR mutant gene. Both types of PKR-deficient cells were more permissive for viral replication than the control U-937 cells. As the result of PKR loss, they also showed impaired induction of IFN-alpha and IFN-beta genes in response to several inducers--specifically, encephalomyocarditis virus, lipopolysaccharide, and phorbol 12-myristate 13-acetate. Interestingly, while IFN-alpha induction by dsRNA was impaired in PKR-deficient cells, IFN-beta induction remained intact. Loss of PKR function also resulted in decreased antiviral activity as elicited by IFN-alpha and, to a greater extent, by IFN-gamma. These results implicate PKR in the regulation of several antiviral activities.

Base Sequence↗
PubMed1996

Site-directed mutagenesis of the double-stranded RNA binding domain of bacterially-expressed sigma 3 reovirus protein.

The affinity of the reovirus sigma 3 protein for double-stranded RNA (dsRNA) is well established, and efforts have been made to identify the amino acids involved in this property. In the present study, we further examined the importance of two basic amino acids motifs, located in the carboxy-terminal third of the protein. Mutants, previously characterized in COS cells, were expressed in bacterial cells using the pET expression system. The capability of the different mutants to interact with dsRNA was then determined by the binding of radiolabeled dsRNA to proteins resolved by SDS-polyacrylamide gel electrophoresis and transferred to nitrocellulose filters. It appears that the most carboxy-terminal motif is absolutely required for the binding but the second motif also contributes to this property. However, only the carboxy-terminal motif is required for normal binding upon removal of the amino-terminal domain of the protein by proteolytic cleavage, a procedure previously shown to increase dsRNA-binding. The basic charges in both motifs are important, while breaking of their potential to adopt an alpha helical configuration does not affect binding efficiency. Furthermore, alanine substitution of a single basic amino acid in the carboxy-terminal motif can be sufficient to strongly reduce the binding of dsRNA to the protein. Altogether, these data suggest that basic amino acids of the sigma 3 carboxy-terminal motif are directly involved in dsRNA binding, while the other basic motif may contribute by preventing an inhibitory effect of the amino-terminal portion of the protein.

Animals↗
PubMed1996

The regulation of the protein kinase PKR by RNA.

A model is presented for the regulation of the double-stranded RNA (dsRNA)-activated mammalian protein kinase PKR, which is involved in protein synthesis inhibition and the antiviral response in cells. A series of previous findings abut PKROs behavior are reviewed, including its effects on translation; the activation of its protein kinase activity; binding sites for PKR on RNA; PKROs protein domains, which include two double-stranded RNA binding motifs (dsRBMs); and the likelihood of PKR dimer formation. The model which emerges to account for many of these observations includes the suggestion that PKR dimers form which are stabilized and rearranged upon binding to dsRNA regions 60 bp or longer. The hypothesis includes protein conformational changes within each member of a PKR dimer bound to dsRNA which re-position an inhibitory polypeptide domain and thus allow kinase activation. Also considered are ways in which PKR interacts with imperfectly duplexed, highly structured RNA molecules.

Animals↗
PubMed1978

Synthesis of an oligonucleotide inhibitor of protein synthesis in rabbit reticulocyte lysates analogous to that formed in extracts from interferon-treated cells.

A heat-stable, low-molecular-weight inhibitor of protein synthesis is formed on incubation of haemin-supplemented rabbit reticulocyte lysates with ATP and double-stranded RNA (dsRNA). It inhibits the translation of both added encephalomyocarditis virus RNA (EMC RNA) and endogeneous messenger RNA in reticulocyte lysates and mouse L-cell extracts. The enzyme responsible for the synthesis of the inhibitor binds to dsRNA and can be purified on a column of poly(I).poly (C) bound to an inert support. The highly purified enzyme in its stable column-bound state can be conveniently employed to synthesise the inhibitor and to label it with [3H]ATP, or [alpha-32P]ATP or [gamma-32P]ATP as substrate. The radioactive inhibitor synthesised in this way with material from rabbit reticulocyte lysates shows the same spectrum of resistance and sensitivity to alkali and a variety of enzymes as corresponding material similarly synthesised with extracts from interferon-treated mouse L-cells. The inhibitors from the two systems have comparable absorbance spectra, are chromatographically and electrophoretically indistinguishable and are apparently identical in specific activity in the inhibition of protein synthesis in the cell-free system. The inhibitor is also formed on inhibition of protein synthesis by dsRNA in reticulocyte lysates. On comparison of the spectrum of polypeptide products synthesised in response to EMC RNA in the reticulocyte lysate, the effects of the inhibitor or dsRNA were similar: a distinctly different effect was obtained with the haemin-controlled repressor, a known inhibitor of initiation. The significance of these results with respect to the mechanism of action of the inhibitor and its role in the inhibition observed in response to dsRNA is discussed.

Adenosine Triphosphate↗
PubMed1975

Polyadenylic acid on poliovirus RNA. III. In vitro addition of polyadenylic acid to poliovirus RNAs.

A crude RNA polymerase preparation was made from HeLa cells infected for 3 h with poliovirus. All virus-specific RNA species labeled in vitro (35S RNA, replicative intermediate RNA [RI], and double-stranded RNA [dsRNA]) would bind to poly(U) filters and contained RNase-resistant stretches of poly(A) which could be analyzed by electrophoresis in polyacrylamide gels. After incubation for 45 min with [3-H]ATP in the presence of the other three nucleoside triphosphates, the labeled poly(A) on the RI and dsRNA migrated on gels as relatively homogenous peaks approximately 200 nucleotides in length. In contrast, the poly(A) from the 35S RNA had a heterogeneous size distribution ranging from 50 to 250 nucleotides. In the absence of UTP, CTP, and GTP, the size of the newly labeled poly(A) on the dsRNA and RI RNA was the same as it was in the presence of all four nucleoside triphosphates. However the poly(A) on the 35S RNA lacked the larger sequences seen when the other three nucleoside triphosphates were present. When [3-H]ATP was used as the label in infected and uninfected extracts, heterogeneous single-stranded RNA sedimenting at less than 28S was also labeled. This heterogeneous RNA probably represents HeLa cytoplasmic RNA to which small lengths of poly(A) (approximately 15 nucleotides) had been added. These results indicate that in the in vitro system poly(A) can be added to both newly synthesized and preexisting RNA molecules. Furthermore, an enzyme capable of terminal addition of poly(A) exists in both infected and uninfected extracts.

Adenine Nucleotides↗
PubMed2003

Poly(I-C)-induced Toll-like receptor 3 (TLR3)-mediated activation of NFkappa B and MAP kinase is through an interleukin-1 receptor-associated kinase (IRAK)-independent pathway employing the signaling components TLR3-TRAF6-TAK1-TAB2-PKR .

Recent studies show that a member of the interleukin-1 (IL-1)/Toll receptor superfamily, Toll-like receptor 3 (TLR3), recognizes double-stranded RNA (dsRNA). Because of the similarity in their cytoplasmic domains, IL-1/Toll receptors share signaling components that associate with the IL-1 receptor, including IL-1 receptor-associated kinase (IRAK), MyD88, and TRAF6. However, we find that, in response to dsRNA, TLR3 can mediate the activation of both NFkappaB and mitogen-activated protein (MAP) kinases in IL-1-unresponsive mutant cell lines, including IRAK-deficient I1A and I3A cells, which are defective in a component that is downstream of IL-1R but upstream of IRAK. These results clearly indicate that TLR3 does not simply share the signaling components employed by the IL-1 receptor. Through biochemical analyses we have identified an IRAK-independent TLR3-mediated pathway. Upon binding of dsRNA to TLR3, TRAF6, TAK1, and TAB2 are recruited to the receptor to form a complex, which then translocates to the cytosol where TAK1 is phosphorylated and activated. The dsRNA-dependent protein kinase (PKR) is also detected in this signal-induced TAK1 complex. Kinase inactive mutants of TAK1 (TAK1DN) and PKR (PKRDN) inhibit poly(dI.dC)-induced TLR3-mediated NFkappaB activation, suggesting that both of these kinases play important roles in this pathway.

Adaptor Proteins, Signal Transducing↗
PubMed2001

Selective binding by the RNA binding domain of PKR revealed by affinity cleavage.

The RNA-dependent protein kinase (PKR) is regulated by the binding of double-stranded RNA (dsRNA) or single-stranded RNAs with extensive duplex secondary structure. PKR has an RNA binding domain (RBD) composed of two copies of the dsRNA binding motif (dsRBM). The dsRBM is an alpha-beta-beta-beta-alpha structure present in a number of proteins that bind RNA, and the selectivity demonstrated by these proteins is currently not well understood. We have used affinity cleavage to study the binding of PKR's RBD to RNA. In this study, we site-specifically modified the first dsRBM of PKR's RBD at two different amino acid positions with the hydroxyl radical generator EDTA.Fe. Cleavage by these proteins of a synthetic stem-loop ligand of PKR indicates that PKR's dsRBMI binds the RNA in a preferred orientation, placing the loop between strands beta1 and beta2 near the single-stranded RNA loop. Additional cleavage experiments demonstrated that defects in the RNA stem, such as an A bulge and two GA mismatches, do not dictate dsRBMI's binding orientation preference. Cleavage of VA(I) RNA, an adenoviral RNA inhibitor of PKR, indicates that dsRBMI is bound near the loop of the apical stem of this RNA in the same orientation as observed with the synthetic stem-loop RNA ligands. This work, along with an NMR study of the binding of a dsRBM derived from the Drosophila protein Staufen, indicates that dsRBMs can bind stem-loop RNAs in distinct ways. In addition, the successful application of the affinity cleavage technique to localizing dsRBMI of PKR on stem-loop RNAs and defining its orientation suggests this approach could be applied to dsRBMs found in other proteins.

Adenoviridae↗
PubMed2001

Cloning of a novel 2',5'-oligoadenylate synthetase-like molecule, Oasl5 in mice.

The 2',5'-oligoadenylate synthetase (2-5OAS) is a enzyme that catalyzes synthesis of 2',5'-oligoadenylates (2-5A) in a dsRNA-dependent manner, and known as a major component of the IFN-induced host defense mechanisms against microbial infections. Here, we report the presence of a novel 2-5OAS-like molecule, termed Oasl5, in mice. The size of Oasl5 cDNA was about 2 kb and encoded a protein consisting of 362 aa. The amino acid sequence showed 76% similarity to the mouse 2-5OAS, however, several motifs being important for the enzyme activity were not conserved. The Oasl5 mRNA was most significantly expressed in the brain, and relatively weak expression was found in other organs such as the spleen, kidney, ovary and testis. It was also expressed in embryonic stem (ES) cells. The Oasl5 mRNA expression in ES cells was elevated 5-fold after treatment with IFN and about 2-fold in the brain when stimulated with IFN inducer, polyinosinic-polycytidylic acid (poly[I:C]). In situ hybridization analysis revealed that Oasl5 is expressed in neurons in the central nervous system in adult mice. When Oasl5 was expressed in E. coli, it yielded 42 kDa protein that binds to dsRNA, but it did not show oligoadenylate synthetase activity. These findings suggest a novel function of Oasl5, which are independent of oligoadenylate synthetase activity, in the brain and developing embryos.

2',5'-Oligoadenylate Synthetase↗
PubMed1998

Cloning, expression, and mapping of ribonucleases H of human and mouse related to bacterial RNase HI.

We identified two human sequences and one mouse sequence in the database of expressed sequence tags that are highly homologous to the N-terminal sequence of eukaryotic RNases H1. The cDNAs for human RNASEH1 and mouse Rnaseh1 were obtained, their nucleotide sequences determined, and the proteins expressed in Escherichia coli and partially purified. Both proteins have RNase H activity in vitro and they bind to dsRNA and RNA-DNA hybrids through the N-terminal conserved motif present in eukaryotic RNases H1. The RNASEH1 gene is expressed in all human tissues at similar levels, indicating that RNase H1 may be a housekeeping protein. The human RNASEH1 and mouse Rnaseh1 cDNAs were used to isolate BAC genomic clones that were used as probes for fluorescence in situ hybridization. The human gene was localized to chromosome 17p11.2 and the mouse gene to a nonsyntenic region on chromosome 12A3. The chromosomal location and possible disease association of the human RNASEH1 gene are discussed.

Amino Acid Sequence↗
PubMed2005

TbMP42, a protein component of the RNA editing complex in African trypanosomes, has endo-exoribonuclease activity.

RNA editing in trypanosomatids is catalyzed by a high molecular mass RNP complex, which is only partially characterized. TbMP42 is a 42 kDa protein of unknown function that copurifies with the editing complex. The polypeptide is characterized by two Zn fingers and a potential barrel structure/OB-fold at its C terminus. Using recombinant TbMP42, we show that the protein can bind to dsRNA and dsDNA but fails to recognize DNA/RNA hybrids. rTbMP42 degrades ssRNA by a 3' to 5' exoribonuclease activity. In addition, rTbMP42 has endoribonuclease activity, which preferentially hydrolyzes non-base-paired uridylate-containing sequences. Gene silencing of TbMP42 inhibits cell growth and is ultimately lethal to the parasite. Mitochondrial extracts from TbMP42-minus trypanosomes have only residual RNA editing activity and strongly reduced endo-exoribonuclease activity. However, all three activities can be restored by the addition of rTbMP42. Together, the data suggest that TbMP42 contributes both endo- and exoribonuclease activity to the editing reaction cycle.

Animals↗
PubMed1996

Identification and analysis of the rnc gene for RNase III in Rhodobacter capsulatus.

The large subunit ribosomal RNA of the purple bacterium Rhodobacter capsulatus shows fragmentation into pieces of 14 and 16S, both fragments forming the functional equivalent of intact 23S rRNA. An RNA-processing step removes an extra stem-loop structure from the 23S rRNA [Kordes, E., Jock, S., Fritsch, J., Bosch, F. and Klug, G. (1994) J. Bacteriol., 176, 1121-1127]. Taking advantage of the fragmentation deficient mutant strain Fm65, we used genetic complementation to find the mutated gene responsible for this aberration. It was identified as the Rhodobacter homologue to mc from Escherichia coli encoding endoribonuclease III (RNase III). The predicted protein has 226 amino acids with a molecular weight of 25.5 kDa. It shares high homology with other known RNase III enzymes over the full length. In particular it shows the double-stranded RNA-binding domain (dsRBD) motif essential for binding of dsRNA substrates. The Fm65 mutant has a frame shift mutation resulting in complete loss of the dsRBD rendering the enzyme inactive. The cloned Rhodobacter enzyme can substitute RNase III activity in an RNase III deficient E. coli strain. Contrary to E. coli, the Rhodobacter mc is in one operon together with the lep gene encoding the leader peptidase.

Amino Acid Sequence↗
PubMed2005

IFN-alpha enhances TLR3-mediated antiviral cytokine expression in human endothelial and epithelial cells by up-regulating TLR3 expression.

TLRs play a critical role in early innate immune response to virus infection. TLR3 together with TLR7 and TLR8 constitute a powerful system to detect genetic material of RNA viruses. TLR3 has been shown to bind viral dsRNA whereas TLR7 and TLR8 are receptors for viral single-stranded RNA. In this report we show that TLR7 or TLR8 are not expressed in human epithelial A549 cells or in HUVECs. Accordingly, A549 cells and HUVECs were unresponsive to TLR7/8 ligand R848. TLR3 was expressed at a higher level in HUVECs than in A549 cells. The TLR3 ligand poly(I:C) up-regulated IFN-beta, IL-28, IL-29, STAT1, and TLR3 expression in HUVECs but not in A549 cells. An enhanced TLR3 expression by transfection or by IFN-alpha stimulation conferred poly(I:C) responsiveness in A549 cells. Similarly, IFN-alpha pretreatment strongly enhanced poly(I:C)-induced activation of IFN-beta, IL-28, and IL-29 genes also in HUVECs. In conclusion, our results suggest that IFN-alpha-induced up-regulation of TLR3 expression is involved in dsRNA activated antiviral response in human epithelial and endothelial cells.

Cell Line, Tumor↗
PubMedDate not supplied

2',5'-oligoadenylate synthetase in interferon-treated chick cells.

Chick embryo cells respond to interferon by producing very high levels of 2-5A synthetase. From inhibitor studies, it appears that the response involves the controlled derepression of an interferon-inducible gene. Continuous interaction of the cells with interferon seems to be necessary to maintain maximal enzyme induction. Partial purification of the synthetase indicates that it is probably composed of a single polypeptide of 56,000 MW. Upon activation by binding to dsRNA, this polypeptide catalyzes a nucleotidyl transferase reaction in which 5'-AMP residues are transferred from ATP to the 2' position of appropriate acceptors. A number of naturally occurring small molecules (in addition to 2-5A itself) that can function as adenylate acceptors have been identified, but the physiological significance of these adenylylation reactions remain to be established.

2',5'-Oligoadenylate Synthetase↗
PubMed2004

Nucleocytoplasmic shuttling of JAZ, a new cargo protein for exportin-5.

Exportin-5 is a nuclear export receptor for certain classes of double-stranded RNA (dsRNA), including pre-micro-RNAs, viral hairpin RNAs, and some tRNAs. It can also export the RNA binding proteins ILF3 and elongation factor EF1A. However, the rules that determine which RNA binding proteins are exportin-5 cargoes remain unclear. JAZ possesses an unusual dsRNA binding domain consisting of multiple C2H2 zinc fingers. We found that JAZ binds to exportin-5 in a Ran-GTP- and dsRNA-dependent manner. Exportin-5 stimulates JAZ shuttling, and gene silencing of exportin-5 reduces shuttling. Recombinant exportin-5 also stimulates nuclear export of JAZ in permeabilized cells. JAZ also binds to ILF3, and surprisingly, this interaction is RNA independent, even though it requires the dsRNA binding domains of ILF3. Exportin-5, JAZ, and ILF3 can form a heteromeric complex with Ran-GTP and dsRNA, and JAZ increases ILF3 binding to exportin-5. JAZ does not contain a classical nuclear localization signal, and in digitonin-permeabilized cells, nuclear accumulation of JAZ does not require energy or cytosol. Nonetheless, low temperatures prevent JAZ import, suggesting that nuclear entry does not occur via simple diffusion. Together, these data suggest that JAZ is exported by exportin-5 but translocates back into nuclei by a facilitated diffusion mechanism.

Active Transport, Cell Nucleus↗
PubMed2001

Ethidium-dependent uncoupling of substrate binding and cleavage by Escherichia coli ribonuclease III.

Ethidium bromide (EB) is known to inhibit cleavage of bacterial rRNA precursors by Escherichia coli ribonuclease III, a dsRNA-specific nuclease. The mechanism of EB inhibition of RNase III is not known nor is there information on EB-binding sites in RNase III substrates. We show here that EB is a reversible, apparently competitive inhibitor of RNase III cleavage of small model substrates in vitro. Inhibition is due to intercalation, since (i) the inhibitory concentrations of EB are similar to measured EB intercalation affinities; (ii) substrate cleavage is not affected by actinomycin D, an intercalating agent that does not bind dsRNA; (iii) the EB concentration dependence of inhibition is a function of substrate structure. In contrast, EB does not strongly inhibit the ability of RNase III to bind substrate. EB also does not block substrate binding by the C-terminal dsRNA-binding domain (dsRBD) of RNase III, indicating that EB perturbs substrate recognition by the N-terminal catalytic domain. Laser photocleavage experiments revealed two ethidium-binding sites in the substrate R1.1 RNA. One site is in the internal loop, adjacent to the scissile bond, while the second site is in the lower stem. Both sites consist of an A-A pair stacked on a CG pair, a motif which apparently provides a particularly favorable environment for intercalation. These results indicate an inhibitory mechanism in which EB site-specifically binds substrate, creating a cleavage-resistant complex that can compete with free substrate for RNase III. This study also shows that RNase III recognition and cleavage of substrate can be uncoupled and supports an enzymatic mechanism of dsRNA cleavage involving cooperative but not obligatorily linked actions of the dsRBD and the catalytic domain.

Base Sequence↗