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

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Query: EC:2.7.7.8 (polynucleotide phosphorylase)
723 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Effect of cAMP on the activity of polynucleotide phosphorylase (PNPase) was studied in polyribosome fraction of rat liver tissue. Intraperitonel administration of cAMP or of theophilline into rats distinctly decreased the PNPase activity in the polyribosome fraction. The cAMP (1-10(-4) M) inhibited the enzymatic activity only by 8% in polyribosome fraction in vitro, as it was estimated by the reaction of phosphorolysis of endogenous RNA and polyA added. Any attempts were proved to be uncucessful to reveal cAMP, ATP-dependent proteinkinase in rat liver, responsible for the decrease in the PNPase activity in the polyribosome fraction. The cAMP inhibited the increase in the PNPase activity, coupled with protein biosynthesis in polyribosomes. Moreover, cAMP caused a decrease in the PNPase activity in reaction of polyA phosphorolysis and did not affect the rate of endogenous RNA phosphorolysis in polyribosome fraction, isolated from postmitochondrial fraction after incubation for 15 min at 30 degrees. The 3',5'-cyclo AMP (2-10(-6)-2-10(-4) M) stimulated incorporation of 14C-leucine into acid-insoluble material, when postmitochondrial fraction was incubated under the same conditions. The data obtained suggest that cAMP either inhibits specifically the PNPase synthesis or represses the coupled with protein biosynthesis formation of active "heavy" type of PNPase from less active "light" type.
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PMID:[Effect of cyclic-3',5'-AMP on rat liver polynucleotide phosphorylase activity]. 18 2

O2-Ethyl-UDP and O4-methyl-UDP have been prepared and copolymerized in various proportions with UDP or CDP, using polynucleotide phosphorylase. The copolymers were used as templates for DNA-dependent RNA polymerases in the presence of Mn2+. Both of the O-alkylated uridines caused a similar misincorporations. When copolymerized with U they led to incorporation of CMP and GMP into the poly(A). No AMP or UMP incorporation seemed to be caused by the introduction of O-alkyluridines into either poly(U) or poly(C). The mispairing of O2- and O4-alkyluridine to behave like C or G represents mutagenic events. O2 alkylation of U or T is, in contrast to O4 alkylation, a relatively frequent result of treatment of double-stranded nucleic acids with N-nitroso alkylating agents. In single-stranded nucleic acids both O2 and O4 alkylations of U and T occur to similar extents. Thus, the observed mutagenic effects of O2 and O4 alkylation of U may be involved in the high carcinogenicity of these alkylating agents.
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PMID:Preparation and template activities of polynucleotides containing O2- and O4-alkyluridine. 27 2

It has been reported earlier that phage Qbeta RNA (Gilvarg, C., Bollum, F.J. and Weissmann, C. (1975) Proc. Natl. Acad. Sci. U.S. 72, 428-432) elongated at its 3' terminus with up to 100 or more AMP residues retained its full infectivity for Escherichia coli spheroplasts, and that the resulting progeny did not inherit the poly (A) appendage. We now show that while poly (A)-Qbeta RNA appears to function normally as messenger for the synthesis of virus-specific proteins it has lost its capacity to serve as template for Qbeta replicase. Template function could be restored by phosphorolysis with polynucleotide phosphorylase. Taken in conjunction, these results imply that after poly (A)-Qbeta RNA enters the spheroplast a host enzyme (perhaps polynucleotide phosphorylase) removes part or all of the adenylate residues prior to replication of the RNA.
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PMID:Evidence for the participation of a host enzyme in the activation of poly (A)-Qbeta RNA as an infectious agent. 110 68

Using the enzymes terminal deoxyribonucleotidyltransferase (EC 2.7.7.31) and polynucleotide phosphorylase (EC 2.7.7.8), we constructed polyriboadenylic acid tracts, approximately 8000 AMP residues long, attached to the 3'-terminus of a synthetic deoxynucleotide. The polyadenylated DNA, termed the "signal strand", was used in a displacement-type nucleic acid probe assay (see pp 1631-6, this issue). A probe-signal strand complex was made by hybridizing the signal strand to a deoxycytidylate-terminal probe DNA. The probe-signal strand complex was immobilized on an oligo (dG)-cellulose support and subsequently displaced from the immobilized hybrid complex with various amounts of analyte DNA. After the displacement procedure, the polyadenylate tracts were converted to ATP by the combined action of polynucleotide phosphorylase and pyruvate kinase. ATP was quantified by a bioluminescence assay with luciferase from Photinus pyralis. Displacement events were also quantified with biotinylated signal strand bound to avidin-conjugated horseradish peroxidase. Such enzyme-amplified assays offer considerable versatility: they may be coupled to a variety of detection systems including colorimetry, fluorimetry, and luminometry.
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PMID:Nonisotopic detection methods for strand displacement assays of nucleic acids. 242 59

An enzyme, purified 300-fold from Escherichia coli infected with bacteriophage T4, catalyzes the conversion of 5'-termini of polyribonucleotides to internal phosphodiester bonds. The reaction requires ATP and Mg(++). For every 5'-(32)P terminus rendered resistant to alkaline phosphatase, an equal amount of AMP and PPi are formed. Various polyribonucleotides are substrates in the reaction; to date, the best substrate is [5'-(32)P]polyriboadenylate. With the latter substrate, no evidence of intermolecular reaction was obtained. However, the 5'-(32)P termini of poly(A) rendered resistant to alkaline phosphatase are also resistant to attack by RNase II, polynucleotide phosphorylase, and low concentrations of venom phosphodiesterase. Since the product formed with poly(A) lacks 3'-hydroxyl ends, as measured with these exonucleases, the enzyme appears to convert linear molecules of polyriboadenylate to a circular form by the intramolecular covalent linkage of the 5'-phosphate end to the 3'-hydroxyl terminus.
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PMID:Purification and properties of bacteriophage T4-induced RNA ligase. 434 72

Antisera specific for two synthetic oligoribonucleotide sequences, AAU and A2U2, were elicited in rabbits. The oligonucleotides were synthesized using polynucleotide phosphorylase under high salt conditions. Each oligomer was isolated by ion exchange chromatography, and was conjugated to bovine serum albumin, and injected into rabbits as an emulsion with complete Freund's adjuvant. The specificities of the resulting sera were analyzed using a modified Farr-type radioimmunoassay employing homologous oligonucleotide-protein conjugates radiolabeled with [3H]acetic anhydride and unlabeled free oligonucleotides as inhibitors. The antiserum elicited by AAU-BSA reacted well with AAU-RSA but a major fraction of the antibodies was directed to determinants of the conjugate that were not present on the free hapten. With respect to the haptenic determinants, AAU was a better inhibitor than any of the constituent mono- or dinucleotides, implying that features of the entire trinucleotide were being recognized. The other members of the A2Un family reacted to about the same extent as AAU, while other trinucleotides required an up to 21-fold higher concn in order to achieve similar inhibition. The most striking aspect of this antiserum was its failure to bind free ApA, although it could bind the ApA-containing oligonucleotides A3, AAG, AAC and A2Un. It seems likely that the ApA sequence in solution does not contain a significant proportion of a conformation present to a great extent in the ApA-containing oligomers. The antiserum elicited by A2U2-BSA was like anti-AAU-BSA in that some of the antibodies were directed against determinants not present on the free hapten. The most striking result of the inhibition experiments was the specificity of the antiserum for members of the A2Un series. When the A2Un series was compared with AA, AMP or any member of the Un series, approximately four orders of magnitude separated the inhibition curves. The poor binding of component mono- and dinucleotides implies that the conformation recognized by the antibody is present only to a significant extent in the trimeric sequence; the equality of binding of AAU with A2U2, A2U3 and A2U4 suggests that this conformation of the triplet is preserved in the longer sequences. These studies demonstrate the utility of immunochemical procedures for the study of oligonucleotide conformation in solution.
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PMID:Antisera specific for the oligoribonucleotide sequences AAU and A2U2 and their recognition of oligonucleotide conformation. 620 Jul 68

Thin-layer chromatography was employed to measure the activity of polynucleotide phosphorylase (PNP-ase) from E. coli during purification and in the resultant preparation. The TLC data were verified with respect to released inorganic orthophosphate and to 14C-AMP incorporation rate. It is concluded that TLC can be used to determine PNP-ase activity in crude extract, at various purification stages and in the final preparation, yielding correct results.
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PMID:[Determination of the activity of a polynucleotide phosphorylase preparation from E. coli]. 635 7

The platelet population of man and rat can be divided into two classes of about equal size on the basis of presence/absence of an acid phosphatase which acts on para-nitrophenylphosphate (a PNPase), at pH 5. The cytochemical reaction product is in the platelet cytoplasmic matrix, without apparent association with organelles or membrane systems. We could not relate differences in staining to differences in function: all cells responded the same to activation by thrombin, ADP, or collagen, in fibrinogen binding to activated platelets, by endocytosis of fluid-phase tracers, and in internalization of latex particles. With respect to possible physiological substrates for the PNP-ase, there was no reaction product from beta-glycerophosphate, AMP, ADP, ATP, GTP, CMP, IMP, cAMP, creatine phosphate, and inositol phosphates, and the enzyme was not inhibited by 40 mM lithium. There was reaction product from tyrosine phosphate suggesting that the physiological substrate for PNP-ase is tyrosine phosphate. In rat bone marrow, megakaryocytes also were of two classes, PNPase positive and PNPase negative, suggesting that different classes of platelets arise from different classes of megakaryocytes.
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PMID:Blood platelet heterogeneity: evidence for two classes of platelets in man and rat. 752 21

Repair of the 3'-terminal -CCA sequence of tRNA generally requires the action of the enzyme tRNA nucleotidyltransferase. However, in Escherichia coli in the absence of this enzyme, a decreased level of tRNA end repair continues. To ascertain the enzymes responsible for this residual repair, mutant strains were constructed lacking tRNA nucleotidyltransferase and other enzymes potentially involved in the process, poly(A) polymerase I and polynucleotide phosphorylase (PNPase). Strains lacking tRNA nucleotidyltransferase and either one of the other enzymes displayed decreased growth rates and increased levels of defective tRNA compared with the single cca mutant. Triple mutants lacking all three enzymes grew very slowly, had even more defective tRNA, and were devoid of activity incorporating AMP into tRNA-C-C. Overexpression of poly(A) polymerase I, but not PNPase, partially compensated for the absence of tRNA nucleotidyltransferase. These data show that poly(A) polymerase I and PNPase participate in the end repair process and are required to maintain functional tRNA levels when tRNA nucleotidyltransferase is absent.
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PMID:Functional overlap of tRNA nucleotidyltransferase, poly(A) polymerase I, and polynucleotide phosphorylase. 940 15

We recently identified polynucleotide phosphorylase (PNPase) as a potential binding partner for the TCL1 oncoprotein. Mammalian PNPase exhibits exoribonuclease and poly(A) polymerase activities, and PNPase overexpression inhibits cell growth, induces apoptosis, and stimulates proinflammatory cytokine production. A physiologic connection for these anticancer effects and overexpression is difficult to reconcile with the presumed mitochondrial matrix localization for endogenous PNPase, prompting this study. Here we show that basal and interferon-beta-induced PNPase was efficiently imported into energized mitochondria with coupled processing of the N-terminal targeting sequence. Once imported, PNPase localized to the intermembrane space (IMS) as a peripheral membrane protein in a multimeric complex. Apoptotic stimuli caused PNPase mobilization following cytochrome c release, which supported an IMS localization and provided a potential route for interactions with cytosolic TCL1. Consistent with its IMS localization, PNPase knockdown with RNA interference did not affect mitochondrial RNA levels. However, PNPase reduction impaired mitochondrial electrochemical membrane potential, decreased respiratory chain activity, and was correlated with altered mitochondrial morphology. This resulted in FoF1-ATP synthase instability, impaired ATP generation, lactate accumulation, and AMP kinase phosphorylation with reduced cell proliferation. Combined, the data demonstrate an unexpected IMS localization and a key role for PNPase in maintaining mitochondrial homeostasis.
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PMID:Mammalian polynucleotide phosphorylase is an intermembrane space RNase that maintains mitochondrial homeostasis. 1696 81


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