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)

Filaments formed by the polymerization of RecA protein along DNA in the presence of Mg2+ and adenosine 5'-0-(3-thiotriphosphate) (ATP gamma S) are seen by electron microscopy to have a 10 nm diameter with a 9 nm helical repeat. When certain preparations of apparently pure RecA protein are incubated with Mg2+ and ATP gamma S in the absence of nucleic acid for extended times, very long filaments with the same 10 nm diameter and 9 nm axial repeat are seen. We show here that these long 10 nm filaments can contain RNA which is present as a contaminant of the RecA protein and poly(A) which is synthesized during the incubations by an activity that is apparently polynucleotide phosphorylase. RecA protein purified by a procedure developed in this laboratory did not contain RNA and did not form these very long 10 nm filaments. However, when exogenous RNA was added to this protein, 10 nm filament formation was observed.
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PMID:10 nm RecA protein filaments formed in the presence of Mg2+ and ATP gamma S may contain RNA. 241 90

We have characterized a chloroplast processing activity that catalyzes the conversion of the plastid cytochrome b6/f subunit IV (pet D) mRNA 3' end precursor to the mature RNA possessing a 3' inverted repeat (IR). In a chloroplast soluble protein extract, the activity requires Mg2+ or Mn2+, but not K+. In the absence of Mg2+, the pet D 3' IR-RNA product does not accumulate, and UV-cross-linking indicates that the 3' IR-RNA precursor binds several new proteins in addition to those previously characterized as part of the 3' IR-RNA: protein complex in vitro. In contrast, high concentrations of Zn2+ or Cu2+ suppress protein binding and inhibit the processing reaction. The purified exoribonuclease polynucleotide phosphorylase (E.C.2.7.7.8) is not efficient in processing the pet D 3' IR-RNA precursor, whereas Escherichia coli ribonuclease II rapidly processes the pet D IR-RNA precursor to a product of a size similar to that of the mature 3' IR-RNA, but also rapidly degrades the mature RNA in the absence of chloroplast extract. We therefore conclude that the maturation of the pet D mRNA in vitro requires specific chloroplast enzymes which process the mRNA 3' end precursor in the absence of efficient transcription termination. The chloroplast enzyme activities are biochemically distinct from their bacterial counterparts. We also note that specific chloroplast components may be required to stabilize the mature pet D mRNA 3' end against further exonucleolytic degradation.
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PMID:Chloroplast mRNA 3' end maturation is biochemically distinct from prokaryotic mRNA processing. 248 89

Novel RNA polymerase activities (termed type II reaction) can be found in toluene-treated Escherichia coli with Ca2+, Fe2+, or endogenously bound cations, probably Mg2+. These activities are distinguishable from the well characterized DNA-dependent RNA polymerase (type I reaction) by: (i) their divalent cation requirements, i.e., the classical enzyme is activated by exogenously added Mn2+, Mg2+, or CO2+ ions; (ii) their relative resistance to inhibition by actinomycin D, rifampicin, and streptolydigin; (iii) their selective synthesis of low molecular weight RNA; (iv) their sensitivity to inhibition by arabinonucleoside 5'-triphosphates or deoxyribonucleoside 5'-triphosphates; and (v) the strict requirement for ATP in Ca2+ and bound cation-activated reactions. The Ca2+-activated and endogenous RNA polymerase activities are inhibited by orthophosphate. The properties of the type II RNA polymerase(s) are compared with those of polynucleotide phosphorylase, and dnaG gene product, and the RNA polymerase described by Ohasa and Tsugita.
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PMID:Divalent cation-activated RNA synthesis in toluene-treated Escherichia coli. 617 Apr 2

1. Polynucleotide phosphorylase [polyribonucleotide: orthophosphate nucleotidyltransferase, EC 2.7.7.8] was purified to near homogeneity from the photosynthetic bacterium, Rhodospirillum rubrum. The purified enzyme had a molecular weight of approximately 160,000, and consisted of two equivalent subunits of approximately 76,000 daltons. It catalyzed the three reactions described below. 2. In the exchange reaction of the beta-phosphate of nucleoside diphosphates with Pi by the purified enzyme in the presence of 3.3 mM Pi, 6.7 mMCl2, and 0.33 mM or 1.0 mM nucleotide at pH 8.0 and 20 degrees C, ADP, GDP, and CDP, and CDP were better substrates than UDP, while IDP and deoxyribonucleoside diphosphates hardly served as substrates. The ADP-Pi exchange activity was significantly inhibited by high concentrations of either ADP or Pi. 3. In the polymerization reaction of ribonucleoside diphosphates by the purified enzyme in the presence of 6.7 mM nucleotide and 6.7 mM MgCl2 at pH 8.0 and 20 degrees C, ADP was the best substrate; the activities relative to that with ADP were 55% with UD, 51% with CDP, and 48% with IDP, while GDP hardly served as a substrate, 4. In the phosphoryolysis reaction of polynucleoside diphosphates by the purified enzyme in the presence of 1.0 mM polynucleotide, 6.7 mM Pi, and 6.7 mM MgCl2 at pH 8.0 and 20 degrees C, poly[U] was the best substrate; the activities relative to that with poly[U] were 32% with poly[A], 28% with poly[I], 21% with poly[C], and 2% with yeast RNA, while poly[G] and yeast DNA hardly served as substrates. 5. The three kinds of activities of the purified enzyme described above were stimulated by divalent cations such as Mg2+, Mn2+, Cd2+, and Co2+.
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PMID:Purification and properties of polynucleotide phosphorylase from photosynthetic bacterium Rhodospirillum rubrum. 676 23

The activity of polynucleotide phosphorylase (PNPase) from rat liver nuclei isolated in aqueous and non-aqueous media was studied. It was shown that aqueous and non-aqueous nuclear preparations differ both in specific activity (106 and 39 units per mg of protein, respectively) and in the enzyme content (11.2 and 3.4% of homogenate activity, respectively). Nuclear PNPase reveals its maximal activity at pH 7.6-8.0 and requires Mg2+. The enzyme catalyzed polyribonucleotide phosphorelysis in the following order: poly (A) leads to poly(U) leads to poly(S) leads to RNA leads to poly(A) . poly(U). It is concluded that a comparatively low PNPase activity of the nuclei isolated in sucrose media is due to the enzyme extraction from the nuclei in the course of isolation.
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PMID:[Polynucleotide phosphorylase from rat liver nuclei. Determination of the activity and some properties]. 729 10

The ADP analogue in which the 5'-oxygen has been replaced by a methylene group can be prepared by condensing 5'-deoxy-5'-phosphonomethyladenosine with inorganic phosphate. This analogue readily polymerizes onto the primer A-A in the presence of the enzyme polynucleotide phosphorylase and either Mg2+ or Mn2+. The initial products are of the form A-A(-cA)n-cA (where "-" and "-c" stand for the normal phosphodiester linkage and the linkage in which the 5'-oxygen is replaced with the methylene group, respectively). Treatment of these with alkali yields adenosine 2'(3')-phosphate and the series (A(-cA)n-cA containing only phosphonomethylene linkages. The decamer A(-cA)8-cA interacts with two molecules of U(-U)8-U to form a triple-standard structure that has a stability similar to that exhibited by the analogous complex formed from A(-A)8-A and U(-U)8-U. This property, along with the resistance of these oligomer analogues toward nucleases that cleave phosphodiester linkages between the phosphorus and the 5'-oxygen, should provide a strong rationale for application of phosphonomethylene linkages in schemes for therapeutic drug design that use the antisense strategy.
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PMID:Synthesis and properties of adenosine oligonucleotide analogues containing methylene groups in place of phosphodiester 5'-oxygens. 839 23

Hammerhead ribozymes are small catalytic RNA molecules that can be designed to specifically cleave other RNAs. These ribozymes have exhibited low efficiency when examined inside cells, perhaps in part because of their sensitivity to intracellular RNases. In an effort to better understand intracellular degradation of small, foreign RNAs and to develop more stable ribozymes, the ability of Escherichia coli RNase mutants to digest ribozymes was examined. In soluble extracts, most (80 to 90%) of the endonucleolytic activity was due to RNases I and I*, since degradative activity was inhibited by Mg2+ and by the rna-2 mutation. Degradation by exonucleolytic activities was temperature sensitive in extracts from an rna pnp rnb(Ts) triple mutant but not in extracts from an rna rnb(Ts) double mutant. Thus, the products of rnb and pnp, RNase II and polynucleotide phosphorylase, respectively, appear to be the major exonucleases that degrade hammerhead ribozymes. Examination of intracellular degradation revealed that RNases I and I* contributed to about half of the degradative activity as judged by comparison of the rate of ribozyme decay in wild-type and rna-2 mutant cells. Little additional effect was observed in rne(RNase E) and rnc (RNaseIII) mutants. Taken together, these data indicate that hammerhead ribozymes are digested largely by the degradative class of RNase (RNases I, I* and II and polynucleotide phosphorylase).
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PMID:RNases involved in ribozyme degradation in Escherichia coli. 862 92

In the presence of Mg2+ ions, polynucleotide phosphorylase (PNPase, EC 2.7.7.8) is known to synthesize RNA-like polymers using ribonucleoside-5'-diphosphate (NDP) substrates but to be unable to utilize deoxyribonucleoside substrates. Our experiments show that when MgCl2 is replaced by FeCl3, PNPase becomes able to synthesize deoxyheteropolymers using deoxyribonucleoside-5'-diphosphates (dNDPs). The deoxyheteropolymer formed from the four dNDPs is degraded by pancreatic DNase, but not by RNase, and is readily used as a template by DNA-dependent DNA polymerase. Synthesis of this DNA-like polymer is accomplished de novo without the help of any primer or preexisting template. What is more, dA/dG and dC/dT ratios of polymers synthesized by different bacterial PNPases closely match ratios found in DNA of the bacterial species the enzyme came from.
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PMID:De Novo Synthesis of DNA-Like Molecules by Polynucleotide Phosphorylase In Vitro 866 1


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