Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.11.1 (protein kinase)
 81,284 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Purified potato spindle tuber viroid (PSTVd) was added to an in vitro assay system containing purified interferon-induced, dsRNA-activated protein kinase (P68). Viroid RNA activated (phosphorylated) the enzyme, although with less efficiency than did the synthetic, perfectly matched poly I-poly C. In binding experiments, RNA transcripts of the intermediate strain of PSTVd were shown to specifically bind to a P68-antibody complex. Activation of the enzyme by a strain of PSTVd that results in severe symptoms in infected tomato plants was at least ten-fold that by the mild strain. Activation by a strain that results in intermediate symptoms was quantitatively similar to activation by the severe strain. To our knowledge, this is the first demonstration of a differential effect of viroid strains inducing different levels of pathology on any biochemical or metabolic system investigated. This differential effect suggests that activation of a plant enzyme homologous to mammalian P68 protein kinase may represent the triggering event in viroid pathogenesis. Differential activation of P68 is surprising, because the primary structures of the mild and severe PSTVd strains analyzed differ by only a two-nucleotide inversion (UUC-->CUU) in the lower portion of the 'pathogenicity' region of the molecules. This change, according to thermodynamic calculations, should have only a minor effect on the secondary structure of the viroid molecule. Binding assays indicated that PSTVd specifically binds to P68.
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PMID:Mechanism of viroid pathogenesis: differential activation of the interferon-induced, double-stranded RNA-activated, M(r) 68,000 protein kinase by viroid strains of varying pathogenicity. 750 21

Control of the interferon-induced double-stranded RNA (dsRNA) activated protein kinase (referred to as P68 because of its M(r) of 68,000 in human cells) by animal viruses is essential to avoid decreases in protein synthetic rates during infection. We have previously demonstrated that poliovirus establishes a unique way of regulating the protein kinase, namely by inducing the specific degradation of P68 during infection (T. L. Black, B. Safer, A. Hovanessian, and M. G. Katze, J. Virol. 63:2244-2251, 1989). In the present study we investigated the mechanisms by which P68 degradation occurred. To do this we used an in vitro degradation assay which faithfully reproduced the in vivo events. Although viral gene expression was required for P68 degradation, the major poliovirus proteases, 2A and 3C, were found not to be directly involved with P68 proteolysis. However, the protease responsible for P68 degradation required divalent cations for maximal activity and probably has both an RNA and a protein component since trypsin and ribonuclease abrogated the activity. Despite this requirement for divalent cations and RNA, activation of the kinase was not required for proteolysis since a catalytically inactive P68 was still degraded. Mapping of P68 protease-sensitive sites by using in vitro translated truncation and deletion mutants revealed that sites required for degradation resided in the amino terminus and colocalized to dsRNA-binding domains. Finally, we found that preincubation of cell extracts with the synthetic dsRNA poly(I-C) largely prevented P68 proteolysis, providing additional evidence for the critical role of RNA. On the basis of these data, we present a hypothetical model depicting possible mechanisms of P68 degradation in poliovirus-infected cells.
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PMID:Degradation of the interferon-induced 68,000-M(r) protein kinase by poliovirus requires RNA. 767 6

Activation of the interferon-inducible 68-kDa protein kinase (referred to as P68) by double-stranded RNA catalyzes phosphorylation of the alpha subunit of eukaryotic protein synthesis initiation factor 2. We have analyzed the transient expression of mutant and wild-type kinase molecules in transfected COS cells to examine the effects of the kinase on gene expression in the absence of other interferon-induced gene products. The wild-type P68 kinase was expressed inefficiently whereas a catalytically inactive P68 was expressed at 30- to 40-fold higher levels. Protein stability measurements and primer-extension analysis of human kinase-specific mRNA levels provided evidence that kinase expression was regulated at the level of mRNA translation. Further, cotransfection experiments revealed that the domain II catalytically inactive mutant could stimulate reporter gene protein synthesis in a transdominant manner. We also examined the expression of mutants with deletions in the N-terminal double-stranded RNA binding domains and found that a kinase construct lacking aa 156-243 was expressed at levels comparable to the wild type whereas a P68 construct lacking aa 91-243 was expressed at levels 70-fold higher. Both the inactive domain II P68 mutant and the deletion mutant lacking aa 91-243 were less inhibitory to growth in yeast due to the reduced ability to phosphorylate initiation factor 2 alpha in vivo. In conclusion we have demonstrated that the P68 kinase can regulate mRNA translation primarily of its own mRNA and to a lesser extent of a heterologous mRNA and that this regulation is notably affected by mutations in either the catalytic or N-terminal regulatory domains.
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PMID:Translational regulation by the interferon-induced double-stranded-RNA-activated 68-kDa protein kinase. 809 44

Viroids are autonomously replicating pathogens of higher plants that consist solely of unencapsidated, single-stranded, circular RNAs of 246-375 nucleotides. Despite their extreme simplicity, viroids cause syndromes in plants that are about as varied as those caused by plant viruses. Because viroids are not translated, their effects on plants must be a consequence of direct interaction of the viroid with host constituents. Although the molecular mechanisms of viroid pathogenesis are still unknown, analysis of molecular chimeras between viroids of different pathogenicity levels has revealed that the severity of symptoms is the result of complex interactions among three of the five viroid domains. In vitro experiments with purified mammalian protein kinase P68 have shown that the enzyme is strongly activated (phosphorylated) by viroid strains that incite moderate to severe symptoms, but far less by a mild strain. Activation of a plant homolog of P68 may be the triggering event in viroid pathogenesis.
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PMID:Viroids: the smallest and simplest agents of infectious disease. How do they make plants sick? 810 11


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