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

---

Query: EC:2.7.7.48 (transcriptase)
9,479 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Heterologous expression of human LINE-1 ORF2 in yeast yielded a single polypeptide (Mr145 000) which reacted with specific antibodies and co-purified with a reverse transcriptase activity not present in the host cells. Various deletion derivatives of the ORF2 polypeptide were also synthesized. Reverse transcriptase assays using synthetic polynucleotides as template and primer revealed that ORF2 protein missing a significant portion of the N-terminal endonuclease domain still retains some activity. Deletion of the C-terminal cysteine-rich motif reduces activity only a small amount. Three non-overlapping deletions spanning 144 amino acids just N-terminal to the common polymerase domain of the ORF2 protein were analyzed for their effect on reverse transcriptase activity; this region contains the previously-noted conserved Z motif. The two deletions most proximal to the polymerase domain eliminate activity while the third, most-distal deletion had no effect. An inactive enzyme was also produced by substitution of two different amino acids in a highly-conserved octapeptide sequence, Z8, located within the region removed to make the deletion most proximal to the polymerase domain; substitution of a third had no effect. We conclude that the octapeptide sequence and neighboring amino acids in the Z region are essential for reverse transcriptase activity, while the endonuclease and cysteine-rich domains are not absolutely required.
...
PMID:The human LINE-1 reverse transcriptase:effect of deletions outside the common reverse transcriptase domain. 967 14

RTE-1 is a non-long-terminal-repeat (non-LTR) retrotransposable element first found in the Caenorhabditis elegans genome. It encodes a 1,024-amino-acid open reading frame (ORF) containing both apurinic-apyrimidic endonuclease and reverse-transcriptase domains. A possible first ORF of only 43 amino acids overlaps with the larger ORF and may be the site of translation initiation. Database searches and phylogenetic analysis indicate that representatives of the RTE clade of non-LTR retrotransposons are found in the bovine and sheep genomes of mammals and in the silkmoth and mosquito genomes of insects. In addition, the previously identified SINEs, Art2 and Pst, from ruminate and viper genomes are shown to be truncated RTE-like retrotransposable elements. RTE-derived SINE elements are also found in mollusc and flatworm genomes. Members of the RTE clade are characterized by unusually short 3' untranslated regions that are predominantly composed of AT-rich trimer, tetramer, and/or pentamer repeats. This study establishes RTE as a very widespread clade of non-LTR retrotransposons. RTE represents the third distinct class of non-LTR retrotransposons in the vertebrate lineage (after Line 1 elements in mammals and CR1 elements in birds and reptiles).
...
PMID:The RTE class of non-LTR retrotransposons is widely distributed in animals and is the origin of many SINEs. 972 77

The influenza virus RNA-dependent RNA polymerase protein complex contains an associated RNA endonuclease activity, which cleaves host mRNA precursors in the cell nucleus at defined positions 9-15 nucleotides downstream of the cap structure. This reaction provides capped oligoribonucleotides, which function as primers for the initiation of viral mRNA synthesis. The endonuclease reaction is dependent on the presence of divalent metal ions. We have used a number of divalent and trivalent metal ions alone and in combination to probe the mechanism of RNA cleavage by the influenza virus endonuclease. Virus-specific cleavage was observed with various metal ions, and maximum cleavage activity was obtained with 100 microM Mn2+ or 100 microM Co2+. This activity was about 2-fold higher than that observed with Mg2+ at the optimal concentration of 1 mM. Activity dependence on metal ion concentration was cooperative with Hill coefficients close to or larger than 2. Synergistic activation of cleavage activity was observed with combinations of different metal ions at varying concentrations. These results support a two-metal ion mechanism of RNA cleavage for the influenza virus cap-dependent endonuclease. The findings are also consistent with a structural model of the polymerase, in which the specific endonuclease active site is spatially separated from the nucleotidyl transferase active site of the polymerase module.
...
PMID:Metal ion catalysis of RNA cleavage by the influenza virus endonuclease. 1022 Mar 50

Influenza is worldwide one of the deadliest infectious diseases. Lethal influenza mutants can unpredictably arise, as in the 1918 pandemic, or in the 1997 Hong Kong influenza outbreak. Vaccines are today the only protective prophylactic agents, and development of potent new anti-influenza drugs of therapeutic effectiveness appears urgent. It is the aim of the present review, to summarize and discuss the different investigational approaches to this goal. In Medline- and several internet virology database-searches, numerous citations were compiled, and selected according to their relevance to the different topics discussed. The antiviral agents are classified according to their target in the viral replication cycle: proteolytic activation of haemagglutinin, attachment of the virus to specific cell-surface receptors, endocytosis and fusion with the endosomal membrane, uncoating of the nucleocapsid, multiplication, i.e. synthesis of viral RNA and mRNA, and release of the new virus generation from the host cell surface. Potential drugs, directed towards each of these replication steps are described with respect to their mechanism of action, antiviral activity, toxic side effects and induction of resistance. The most promising candidates for safe and potent new influenza drugs, are antiviral agents, directed towards a virus-specific, well conserved target, such as inhibitors of virus-cell fusion, inhibitors of RNA transcriptase and endonuclease, and inhibitors of neuraminidase. It can be hoped that in the near future potent and therapeutically effective anti-influenza drugs will be available.
...
PMID:Influenza chemotherapy: a review of the present state of art and of new drugs in development. 1120 14

The influenza virus polymerase complex contains two associated enzymatic activities, an endoribonuclease and a RNA-dependent RNA polymerase activity. Both activities have so far been observed only with the complete polymerase complex consisting of three subunits, PB1, PB2, and PA. This chapter describes a robust and optimized procedure for the purification of active influenza virus polymerase in complex with genomic RNA and the single-stranded RNA-binding protein nucleoprotein from influenza virus particles. It also explains the synthesis of capped RNA molecules as substrates of the influenza virus endonuclease. The enzymatic properties of influenza virus-derived endoribonuclease activity have been characterized with a model RNA substrate of 20-nucleotide length, termed G20 RNA. The rate of RNA cleavage under steady state conditions appears to be limited by product dissociation. Therefore conditions have been optimized to study the chemical step of RNA cleavage under single turnover conditions. The enzyme requires divalent metal ions for activity and can use Mn(II), Co(II), and Fe(II) efficiently at pH 7, Mg(II) with intermediate efficiency, and Ni(II) and Zn(II) with lower efficiency. The reaction progress curves show slow binding of Zn(II) and Ni(II) to the protein, suggesting a conformational change of the active site as a prerequisite for endonuclease activity in the presence of these two metal ions. Low concentrations of the detergent DOC inhibit the activity and also disrupt the trimeric polymerase complex, whereas other detergents do not have a significant effect on the activity.
...
PMID:Influenza virus endoribonuclease. 1158 17

The influenza A virus RNA-dependent RNA polymerase catalyzes several reactions in transcription and replication of the genome RNA. The first step in viral mRNA synthesis is the endonucleolytic cleavage of host cell mRNAs containing a cap structure to generate capped primers that are 10-14 nucleotides long which are then used to prime transcription of virus-specific mRNAs. To analyze the properties of the capped RNA-specific endonuclease associated with the influenza virus polymerase and the roles of each of the three subunits in transcription initiation, we established an in vitro assay to investigate this endonucleolytic cleavage reaction. This assay consists of an artificial RNA substrate containing a cap-0 structure at its 5' end and a partial alfalfa mosaic virus RNA 4 (AIMV RNA 4) sequence which had been shown to be cleaved by the influenza polymerase. Results showed that purified virion ribonucleoprotein complexes cleaved the RNA substrate specifically to generate a capped 14-nt RNA fragment for use as primer to initiate viral mRNA synthesis. Purified polyclonal anti-PB2 IgG inhibited the endonuclease activity, but anti-PB1 and anti-PA antibodies did not inhibit the cleavage. Partially purified trimeric polymerase expressed by recombinant baculovirus in insect cells cleaved the artificial substrate, but if one or two subunits were removed from the polymerase complex, the cleavage activity was totally lost. Our results suggest that viral PB2 protein is the endonuclease that cleaves host cell mRNA to produce the primer used to initiate transcription; however, association with the other two enzyme subunits seems to be required for this PB2 function.
...
PMID:Influenza A virus RNA polymerase subunit PB2 is the endonuclease which cleaves host cell mRNA and functions only as the trimeric enzyme. 1183 24

Nucleosomal DNA fragmentation is detected in myoblasts only when apoptosis is induced under differentiating conditions. However, the molecular mechanisms and the DNase responsible for the differentiation-dependent apoptotic DNA laddering are poorly understood. Here we show that a Ca(2+)/Mg(2+)-dependent endonuclease, DNase gamma, is induced in C2C12 myoblasts during myogenic differentiation and catalyzes apoptotic DNA fragmentation in differentiating myoblasts. A Ca(2+)/Mg(2+)-dependent, Zn(2+)-sensitive endonuclease activity appears in C2C12 myoblasts during myogenic differentiation. The enzymatic properties of the inducible DNase were found to be quite similar to those of DNase I family of DNases. Reverse transcriptase-PCR analysis revealed that the induction of DNase gamma, a member of the DNase I family of DNases, is correlated with the appearance of inducible DNase activity. The induction of DNase gamma occurs simultaneously with myogenin induction but precedes the up-regulation of p21. A high level of DNase gamma expression was also detected in differentiated myotubes but not in skeletal muscle fibers in which DNase X is highly expressed. The role of DNase gamma in myoblast apoptosis was evaluated in the following experiments. Proliferating myoblasts acquire DNA ladder producing ability by the ectopic expression of DNase gamma, but not DNase X, suggesting that the expression level of DNase gamma is the determinant of the differentiation-dependent apoptotic DNA laddering observed in myoblasts. DNA fragmentation during differentiation-induced apoptosis is strongly suppressed by the antisense-mediated down-regulation of DNase gamma. Importantly, the extent of DNA laddering is well correlated with the level of endogenous DNase gamma activity. Our data demonstrate that DNase gamma is the endonuclease responsible for DNA fragmentation in apoptosis associated with myogenic differentiation.
...
PMID:Involvement of DNase gamma in apoptosis associated with myogenic differentiation of C2C12 cells. 1205 Jan 66

The influenza A virus RNA-dependent RNA polymerase consists of three subunits-PB1, PB2, and PA. The PB1 subunit is the catalytically active polymerase, catalyzing the sequential addition of nucleotides to the growing RNA chain. The PB2 subunit is a cap-binding protein that plays a role in initiation of viral mRNA synthesis by recruiting capped RNA primers. The function of PA is unknown, but previous studies of temperature-sensitive viruses with mutations in PA have implied a role in viral RNA replication. In this report we demonstrate that the PA subunit is required not only for replication but also for transcription of viral RNA. We mutated evolutionarily conserved amino acids to alanines in the C-terminal region of the PA protein, since the C-terminal region shows the highest degree of conservation between PA proteins of influenza A, B, and C viruses. We tested the effects of these mutations on the ability of RNA polymerase to transcribe and replicate viral RNA. We also tested the compatibility of these mutations with viral viability by using reverse-genetics techniques. A mutant with a histidine-to-alanine change at position 510 (H510A) in the PA protein of influenza A/WSN/33 virus showed a differential effect on transcription and replication. This mutant was able to perform replication (vRNA-->cRNA-->vRNA), but its transcriptional activity (vRNA-->mRNA) was negligible. In vitro analyses of the H510A recombinant polymerase, by using transcription initiation, vRNA-binding, capped-RNA-binding, and endonuclease assays, suggest that the primary defect of this mutant polymerase is in its endonuclease activity.
...
PMID:A single amino acid mutation in the PA subunit of the influenza virus RNA polymerase inhibits endonucleolytic cleavage of capped RNAs. 1218 83

RNA silencing phenomena were first discovered in plants, yet only the RNA interference pathway in animals has been subject to biochemical analysis. Here, we extend biochemical analysis to plant RNA silencing. We find that standard wheat germ extract contains Dicer-like enzymes that convert double-stranded RNA (dsRNA) into two classes of small interfering RNAs, as well as an RNA-dependent RNA polymerase activity that can convert exogenous single-stranded RNA into dsRNA. In this plant embryo extract, an endogenous microRNA (miRNA) that lacks perfect complementarity to its RNA targets nonetheless acts as a small interfering RNA. The miRNA guides an endonuclease to cleave efficiently wild-type Arabidopsis PHAVOLUTA mRNA, but not a dominant mutant previously shown to perturb leaf development. This finding supports the view that plant miRNAs direct RNAi and that miRNA-specified mRNA destruction is important for proper plant development. Thus, endonuclease complexes guided by small RNAs are a common feature of RNA silencing in both animals and plants.
...
PMID:A biochemical framework for RNA silencing in plants. 1287 10

L protein of hantaviruses is the RNA transcriptase and replicase that transcribes mRNAs and replicates the genomic RNA using antigenomic RNA as an intermediate. It also appears to have endonuclease activity. In this review, the current knowledge on the hantavirus L protein is presented including sequence motifs conserved in RNA polymerases, mechanisms of RNA synthesis and also the most recent findings on homologous RNA recombination and membrane association.
...
PMID:L protein, the RNA-dependent RNA polymerase of hantaviruses. 1550 19


<< Previous 1 2 3 4 5 6 7 8 Next >>

---