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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)

Oligoribonucleotides of a predetermined base sequence beginning with adenylyl-3', 5'-adenosine at the 5' end have been synthesized in yields varying between 13% and 42%. The synthesis was carried out using primer-independent polynucleotide phosphorylase from E. coli in the presence of high concentrations of primer and of sodium chloride.
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PMID:Specific oligoribonucleotide synthesis using primer-independent polynucleotide phosphorylase. 17 64

The enzymatic polymerization by polynucleotide phosphorylase of 6-chloro-9-(beta-D-ribofuranosyl)purine 5'-diphosphate to poly(6-chloropurinylic acid) and its conversion to poly(6-thioninosinic acid) is described. The sulfur isostere of poly(I) was found not to form a complex with poly(C), but to form a self-association complex with a Tm around 295 degrees K. The sedimentation velocities, pKa and Tm values of the polymer have been examined under various conditions. A two (or more) stranded helical array is suggested as the most probable structure. Thermal loss of the thione chromophore was noted for poly- (S6I), S6IMP and S6I; the degradation product from S6I was shown to be inosine.
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PMID:Combined enzymatic and chemical approaches to the synthesis of unique polyribonucleotides. 17 53

The complexed 70S ribosomes (monosomes) that accumulate in Escherichia coli after an energy source shift-down were examined in an electron microscope. In all cases, the ribosomes lie at or near one end of a ribonucleic acid (RNA) strand. This messenger RNA (mRNA) has a mean length of 168 nm and a length-average length of 200 nm, sufficient to code for polypeptides of a weight-average molecular weight of 20,000. The length distribution indicates that these strands are a reasonable representation of the population of monocistronic mRNA's of E. coli. The mRNA strands disappear entirely upon digestion with pancreatic ribonuclease, phosphodiesterase I, or polynucleotide phosphorylase. The susceptibility to digestion by 3'-exonucleases indicate that the ribosomes lie at the 5' end of the mRNA strands. These results are consistent with the hypothesis that down-shifted cells have a translational defect at a point subsequent to the binding of ribosomes to mRNA but prior to the formation of the first peptide bond, such that ribosomes remain bound at or near their points of initial attachment to mRNA.
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PMID:Association of messenger ribonucleic acid with 70S monosomes from down-shifted Escherichia coli. 17 81

The polyadenylate [poly(A)] content of the genome RNA of human rhinovirus type 14 (HRV-14) is nearly twice as large as that of the genome RNA of poliovirus type 2. The poly(A) content of viral RNA was determined to be the RNase-resistant fraction of 32P-labeled viral RNA extracted from purified virions. Polyacrylamide gel electrophoresis indicated that the poly(A) sequences of HRV-14 are more heterogenous and on an average larger than those of poliovirus RNA. On the basis of susceptibility to micrococcal polynucleotide phosphorylase the rhinovirus genome terminates in poly(A). Replication of both viruses is almost totally inhibited by cordycepin at 50 mug/ml. At lower concentrations, rhinovirus replication is more sensitive to cordycepin than poliovirus replication. Addition of cordycepin (75 mug/ml) to infected culture prior to or during viral RNA replication results in more or less complete inhibition of virus-specific RNA synthesis. The results do not indicate that cordycepin sensitivity of either virus is due to preferential inhibition of viral poly(A) synthesis by this antibiotic.
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PMID:Polyadenylate sequences of human rhinovirus and poliovirus RNA and cordycepin sensitivity of virus replication. 18 11

We report here the presence of two enzymatic activities associated with highly purified preparations of polynucleotide phosphorylase from Micrococcus luteus. The first, a nuclease activity, which is not separated from the phosphorylase on hydroxylapatite, may be due to substitution of H2O for phosphate in the phosphorolysis reaction. The second activity, a deoxyadenylate kinase, the bulk of which is not resolved from the phosphorylase using gel filtration, sucrose density gradient centrifugation, DEAE-Sephadex, or hydroxylapatite chromatography, may represent a new activity of polynucleotide phosphorylase or be due to an enzyme which is tightly bound to the phosphorylase. Several properties of the kinase are described and its possible significance with respect to the overall enzyme mechanism is discussed.
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PMID:A deoxyadenylate kinase activity associated with polynucleotide phosphorylase from Micrococcus luteus. 18 14

The deoxyribooligonucleotide, d(pT-T-A-G-C-A-G-A-A-C-C-G-G), constituting a segment of yeast iso-1-cytochrome c gene, has been synthesized by a combination of chemical and primarily enzymatic methods. The starting primer, d(pT-T-A-G1, was chemically synthesized by the phosphodiester method and was extended stepwise, by reactions catalyzed by polynucleotide phosphorylase.
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PMID:Enzymatic synthesis of oligonucleotides of defined sequence: synthesis of a segment of yeast iso-1-cytochrome c gene. 18 17

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

Specific activity and level of polynucleotide phosphorylase (PNPase) in polyribosomes of regenerating liver of adult rats, liver of newborn rats and in malignant tumours of rat (sarcoma M-1 and hepatoma 27) were studied. 24 hours after partial hepatectomy the specific activity and level of PNPase in regenerating liver decreased 3--4 times in the fraction of polyribosomes, bound to the endoplasmic reticulum membranes, and remained at a constantly low level in the fraction of free polyribosomes. The PNPase activity also showed a sharp decrease in the fraction of membrane-bound polyribosomes from newborn rats liver and could not be detected either in free or in bound polyribosomes from sarcoma M-1 or hepatoma 27. The PNPase activity in the fraction of bound polyribosomes increased with a decrease in the rate of liver growth (regenerating liver and newborn rats liver), and reached the level normal for adult animals. Possible mechanisms of regulation of the PNPase activity in animal tissue were studied. It was found that a 2-fold administration of cyclic 3,5'-AMP to intact animals (5 mg per 100 g of body weight) with an interval of 8 hours, corresponding to the interval between two peaks of the increase in cyclic 3,5'-AMP concentration following partial hepatectomy, diminished the PNPase specific activity in polyribosomes by 30%. A factor, presumably of protein origin, which induced a release of PNPase from polyribosomes of normal rat liver but did not affect the activity of the liberated enzyme, was detected in the cell sap of sarcoma M-1 and hepatoma 27.
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PMID:[The activity of polynucleotide phosphorylase in polyribosomes of regenerating liver of adult rats, liver of newborn rats and in some reinoculated tumours]. 19 Nov 6

An isotopic shift of the (31)P nuclear magnetic resonance due to (18)O bonded to phosphorus of 0.0206 ppm has been observed in inorganic orthophosphate and adenine nucleotides. Thus, the separation between the resonances of (31)P(18)O(4) and (31)P(16)O(4) at 145.7 MHz is 12 Hz and, in a randomized sample containing approximately 50% (18)O, all five (16)O-(18)O species are resolved and separated from each other by 3 Hz. Not only does this yield the (18)O/(16)O ratio of the phosphate but, more important, the (18)O-labeled phosphate in effect can serve as a double label in following phosphate reactions, for oxygen in all cases and for phosphorus, provided the oxygen does not exchange with solvent water. Thus, it becomes possible to follow labeled phosphorus or labeled oxygen continuously as reactions proceed. Rate studies involving (i) phosphorus and (ii) oxygen are illustrated by continuous monitoring of the exchange reactions between (i) the beta phosphate of ADP and inorganic phosphate catalyzed by polynucleotide phosphorylase and (ii) inorganic orthophosphate and water catalyzed by yeast inorganic pyrophosphatase. In the ADP-P(i) exchange, the P(i) ((18)O(4)) yielded an alpha P((16)O(3) (18)O) and a beta P((18)O(4)), proving that bond cleavage occurs between the alpha P and the alpha-beta bridge oxygen. Among the many additional potential uses of this labeling technique and its spectroscopic observation are: (i) different labeling of each phosphate group of ATP, (ii) to follow rate of transfer of (18)O from a nonphosphate compound such as a carboxylic acid to a phosphate compound, and (iii) to follow the rate of scrambling (for example, of the beta-gamma bridge oxygen of ATP to nonbridge beta P positions) and simultaneously the rate of exchange of the gamma P nonbridge oxygens with solvent water in various ATPase reactions.
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PMID:Isotopic (18O) shift in 31P nuclear magnetic resonance applied to a study of enzyme-catalyzed phosphate--phosphate exchange and phosphate (oxygen)--water exchange reactions. 20 29

This report describes structural studies on purified polynucleotide phosphorylase from C. perfringens. A method is described for the purification of the enzyme which yields a product equivalent in activity to the native polynucleotide phosphorylase from E. coli. These studies revealed a molecular heterogeneity arising from successive stages of proteolysis, to which this enzyme is especially sensitive; unusally, the enzyme is obtained as a mixture of variable proportions of the native and proteolysed forms. We found in all cases a trimeric basic structure composed of the native (alpha) or proteolysed (lapha) or proteolysed (alpha', alpha") catalytic sub-units, However, the enzyme is rather easily dissociated into its sub-units, a phenomenon which seems to accompany proteolysis (Table). Under the action of either endogenous proteases or trypsin, two enzymatic forms are obtained: their quaternary structures seem analogous, but they differ in their catalytic properties from each other and from the initial enzyme. With some care at each step of purification, the polynucleotide phosphorylase of E. coli can be obtained exclusively in its native form. The greater susceptibility to proteolysis of the enzyme from C. perfrigens and the relationship between such degradation and quaternary structure seem to be at the origin of the peculiar behavior of this polynucleotide phosphorylase.
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PMID:[Quaternary structure and proteolysis of the polynucleotide phosphorylase from C. perfringens]. 21 36


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