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At least 433 records · Page 24Linked to original sources
PubMed1984

Inhibition of endoribonuclease VI from Artemia larvae by cytidine 2'-phosphate.

The endoribonuclease VI from Artemia larvae is non-competitively inhibited by cytidine 2'-phosphate with a Ki ca 1 microM. Neither of the cytidine monophosphates isomers with the phosphate group in the 3' or 5' position nor the cyclic 2':3' phosphate are inhibitors at concentrations up to 100 microM. Adenosine, guanosine and uridine 2' or 3' phosphates are also ineffective in this range of concentrations. Certain polyribonucleotides are potent competitive inhibitors of the ribonuclease activity.

Artemia↗
PubMed1980

Binding of quinoline to nucleic acid in a subcellular microsomal system.

Quinoline, a hepatocarcinogen in rats and mutagen in Salmonella typhimurium, binds to RNA, DNA and certain polyribonucleotides in the presence of NADPH and rat liver microsomes. The binding was pronounced with the help of liver microsome preparations made from the rats pretreated with some inducers of the microsomal monooxygenase system. The binding reaction required NADPH and was inhibited by carbon monoxide or aniline, and also by 7,8-benzoflavone, methyrapone or SKF 525A. These results suggested that the cytochrome P-450-linked monooxygenase system is involved in this binding process. Quinoline bound preferably to poly(A), poly(C), poly(G) and poly(X), but negligibly to poly(U) and poly(I). Most of the quinoline residues of the adducts, regardless of the kind of polynucleotides used, were released by acid or alkali at 100 degrees C in the form of 3-hydroxyquinoline. This suggests that 2,3- or 3,4-epoxy derivative of quinoline is the reactive intermediate for nucleic acid modification.

Animals↗
PubMed1990

Photochemical covalent binding of urocanic acid to polynucleic acids.

Photolysis of E-[ring-2-14C]urocanic acid (UA) with native or denatured calf thymus DNA leads to covalent binding of the radiolabel to the nucleic acid. A similar observation is made upon photolysis of the labeled UA with the polyribonucleotides, in which case a strong preference is observed for binding to poly[U]. DNA or poly[U], which had been reacted with UA and purified by dialysis and multiple precipitations, releases UA upon further irradiation with 254 nm light (as expected for cyclobutane adducts). Quantum efficiencies for binding of the UA to native DNA have been measured at 308 and 266 nm and are 0.30 x 10(-5) and 1.3 x 10(-4), respectively, at comparable reactant concentrations. The large increase at the shorter wavelength (where DNA absorption is more competitive) is taken as evidence for the primary role of a DNA excited state in initiating the binding reaction(s).

Animals↗
PubMed1991

Ribonuclease activity and substrate preference of human eosinophil cationic protein (ECP).

The eosinophil cationic protein (ECP), a potent helminthotoxin with considerable neurotoxic activity, was recently shown to also have ribonucleolytic activity. In this work the substrate preference of ECP ribonuclease action was studied in detail. With single-stranded RNA or synthetic polyribonucleotide substrates ECP showed significant but low activity, 70- to 200-fold less than that of bovine RNase A. ECP hydrolyzed RNA more rapidly than it did any synthetic polynucleotide. Poly(U) was degraded more rapidly than poly(C), and poly(A) and double-stranded substrates were extremely resistant. Defined low molecular weight substrates in the form of the 16 dinucleoside phosphates (NpN') and uridine and cytidine 2',3'-cyclic phosphates were tested, and none showed hydrolysis by ECP at a significant rate. The results link ECP ribonucleolytic activity to the 'non-secretory' liver-type enzymes rather than to the 'secretory' pancreatic-type RNases.

Blood Proteins↗
PubMed1995

Photoaquation of cis-dichlorobis-(1,10-phenanthroline)chromium(III) and the photochemical and thermal reactions of this complex with native calf-thymus DNA.

The photoaquation of the title compound [cis-Cr(phen)2CL+2] has been studied using high performance liquid chromatography. Both monoaquo [cis-Cr(phen)2Cl(OH2)2+2] and diaquo [cis-Cr(phen)2(OH2)3+2] products are formed, and the quantum efficiency for the loss of starting material in Tris buffer (pH 7) under argon and oxygen is 0.010 +/- 0.001 and 0.0026 +/- 0.0002, respectively. The presence of deoxyguanosine (dG) increases the rate of loss, as much as twofold under argon, but only the rate of diaquo product formation is enhanced by the nucleoside. The dG effect is attributed to reductive quenching of the cis-Cr(phen)2Cl+2 excited state by the base. Equilibrium dialysis studies indicate that both cis-Cr(phen)2Cl+2 and cis-Cr(phen)2(OH2)3+2 minimally associate with calf-thymus DNA. However, photolyses of cis-Cr(phen)2Cl+2 with the nucleic acid yield a mixture of unidentified covalent adducts. The diaquo complex also forms covalent adducts with DNA in the absence of light. Photolyses of the cis-Cr(phen)2Cl+2 with polyribonucleotides indicate a clear preference for covalent binding to the purines.

Animals↗
PubMed1983

Interactions of nuclear estrogen receptor with DNA and RNA.

The interaction of the nuclear estrogen receptor from hen oviduct with nucleic acids were studied by competition assay using DNa-cellulose centrifugation. We demonstrated that the estradiol-receptor complex binds similarly well to poly(A) RNA and denatured DNA. The estrogen receptor was found to interact more strongly with poly(G), poly(U) than with poly(A), poly(C). The receptor complex binds similarly to poly(A) and poly(dA), and to poly(U) and poly(dU). However, the receptor complex shows stronger binding to poly(G) than to poly(dG) and to poly(C) than to poly(dC). Studies with heteropolyribonucleotides indicated that poly(U1G1) is more effective in competing for the estrogen receptor, and poly(AC) and poly(AUG) are moderately effective, whereas poly(ACU) is least effective. GMP and dGMP showed some competition for the nuclear receptor at 300-fold higher nucleotide concentrations than that of the synthetic poly(G). Observations that the nuclear estrogen receptor binds to poly(A) RNA and interacts selectively with polyribonucleotides suggest that the estrogen receptor-RNA interaction may play a role for the function of estrogens in gene regulation.

Animals↗
PubMed1984

Interaction of rat prostate androgen receptors with polynucleotides, RNA, DNA and cloned DNA fragments.

Androgen receptors were partially purified from prostates of mature (non-castrated) rats by chromatography on 2',5'-ADP-Sepharose and labelled by exchange with 5 alpha-[3H]dihydrotestosterone. The partially purified receptor preparation was free of DNAase activity and sedimented at approx. 3 S. The specificity of the interaction of this androgen receptor with nucleotides was investigated in a competitive binding assay using inhibition of binding of the steroid receptor complex to ADP-Sepharose. Certain polyribonucleotides were strongly bound (e.g., poly(UG), poly(AU), poly(G) and poly(U] and competed more effectively for the receptor binding sites than prostate RNA. Restriction fragments of genomic clones from the genes which code for prostatic binding protein showed only moderate affinity for the 3 S receptor form. These data suggest that the 3 S form of the androgen receptor lacks the specific domain or conformation necessary for specific interaction with DNA, but retains a high affinity for certain forms of RNA. Some potent inhibitors of proteolysis (diisopropylfluorophosphate, leupeptin) did not have any effect on the form of the receptor isolated from mature intact animals. A possible function of the 3 S form in post-transcriptional processing is discussed.

Adenosine Diphosphate↗
PubMed1985

Preparation and properties of highly-purified Vibrio costicola polynucleotide phosphorylase.

Vibrio costicola polynucleotide phosphorylase (polyribonucleotide: orthophosphate nucleotidyltransferase, EC 2.7.7.8) has been purified to electrophoretic homogeneity. It has an approximate molecular weight of 220 000 and consists of identical subunits with an approximate molecular weight of 72 000. The enzyme appears to be a fairly typical polynucleotide phosphorylase with respect to its pH optima, substrate specificity and requirement for a divalent cation cofactor. However, the effect of salt concentration on its physiologically important phosphorolysis activity suggests that it is a moderately halophilic enzyme, able to function at the intracellular ionic strength of the bacterium. In addition, its ADP polymerization activity is remarkably stimulated by polylysine.

Adenosine Diphosphate↗
PubMed1987

Biochemical research on oogenesis: protein synthesis by purified 42S particles from Xenopus laevis and Tinca tinca previtellogenic oocytes.

When incubated with ATP and a labeled amino acid, the 42S particles from early oocytes of Xenopus laevis and Tinca tinca incorporate radioactivity into tRNA and into a high molecular mass material which can be identified as protein. This incorporation is totally independent of ribosomes of cytosolic, mitochondrial or bacterial origin. The incorporated amino acids are linked to a broad spectrum of proteins by covalent bonds. Simple treatments such as incubation in buffer or addition of synthetic polyribonucleotides can inhibit the protein-labeling activity of the particles without affecting their tRNA aminoacylation activity. The former activity corresponds either to an amino acid polymerization reaction or to a protein-modifying reaction of a novel type. No involvement of mRNA in this process has been demonstrated. The alleged amino acid polymerization activity of the 42S particles could be a consequence of the conditions provided to aminoacyl tRNA by the tRNA-binding sites of the particles. These conditions are likely to allow the peptidyl transfer reaction to take place, although at a much lower rate than in the ribosome.

Adenosine Triphosphate↗
PubMed1978

Physical properties of poly (3,N4-ethenocytidylic acid).

Homopolymers of etheno CMP have been prepared by the action of polyribonucleotide phosphorylase upon etheno CDP. At alkaline pH the optical properties are consistent with a structure consisting of partially helical single-stranded chains whose helical regions are stabilized by base stacking. At acid pH the degree of helicity increases markedly. The degree of cooperativity displayed by the helix leads to coil transition induced by pH or temperature is less than for the case of polyribocytidylic acid. In the presence of acridine orange the alkaline form develops a strong extrinsic CD spectrum.

Acridines↗
PubMed1984

In vivo and in vitro binding of epichlorohydrin to nucleic acids.

Epichlorohydrin (EC) binds to macromolecules of biological relevance in vivo: DNA is less labelled than RNA and proteins, rat organs interact more than mouse organs, stomach is the most labelled organ with liver, kidney and lung involved in decreasing order. Based on the Covalent Binding Index (CBI), EC is a weak-moderate oncogen, just as other chlorinated hydrocarbons such as 1,2-dichloroethane and carbon tetrachloride. An interaction of EC with nucleic acids (DNA and polyribonucleotides) occurs also in vitro. It is mediated either by chemical reactivity per se of the molecule (near-UV (NUV) irradiation does not photoactivate EC) and by enzymatic (microsomal and/or cytosolic) fractions, whose relative effectiveness is variable in relation to the organ tested. The best substrates for interaction are poly(G) and poly(A) when using microsomal and cytosolic fractions, respectively, whereas the labelling of double-stranded DNA is always lower. On the whole, the picture of enzyme (microsome + cytosol)-mediated in vitro interaction is similar to the pattern of in vivo binding, with the exception of rat stomach enzymes which are inactive in vitro.

Animals↗
PubMed1995

Protective effect of LPS and poly A:U against immune oxidative injury: role of thiols released by activated macrophages.

Oxidative injury of immune cells has been observed both at inflammatory sites and in pathologic situations, such as human immunodeficiency virus infection. We used an ex vivo model of immune oxidative injury to test the antioxidant effect of two immunomodulating agents administered to C57B1/6 mice. Lipopolysaccharide (LPS) and the synthetic polyribonucleotide poly A:U preserved the ConA-induced proliferative response of spleen T cells against oxidative injury ex vivo. The glutathione and thiol contents of fresh spleen T cells from LPS- and poly A:U-treated mice were significantly higher than control values. In addition, spleen T cells from LPS- and poly A:U-treated mice were protected against the oxidative injury-induced decrease in glutathione content after 48 h of ConA stimulation. Because LPS and poly A:U both activate macrophages, we sought an antioxidant effect of macrophage-released compounds. Neither rhIL-1 alpha nor rhTNF alpha protected against oxidative injury in vitro. In contrast, LPS and poly A:U induced macrophages to release acid-soluble thiols, which have been reported to participate in the regulation of glutathione levels in lymphocytes and could therefore protect against immune oxidative injury.

Animals↗
PubMed2002

Polynucleotide phosphorylase binds to ssRNA with same affinity as to ssDNA.

Polynucleotide phosphorylase (PNPase, polyribonucleotide nucleotidyltransferase, EC 2.7.7.8) is a multifunctional protein, with a 3'-5' processive exoribonuclease, a Pi exchange, an RNA polymerase and an autoregulatory activity. The interaction between this enzyme and the mRNA target is crucial for its activities. In the present study, we characterized the interaction of PNPase with its mRNA regulatory region and ssRNA, as well as with ssDNA and dsDNA by determining K(d). Our results indicate that PNPase has high affinity for its mRNA, ssRNA and for ssDNA (K(d) approximately 10-20 nM). However, this enzyme exhibits a lower affinity for dsDNA (K(d) approximately 200-1400 nM). Possible implications of these results on the molecular mechanisms by which PNPase is regulated and degrades mRNA are discussed.

5' Untranslated Regions↗
PubMed1975

The binding of dimethylnitrosamine to nucleic acids catalyzed by liver enzymic fractions.

The in vitro binding of a metabolite of dimethylnitrosamine (DMNA) to calf thymus DNA catalyzed by a microsomal system from rat liver is reported. The amount ob binding is unaffected by using microsomes induced by 3-methylcholanthrene and/or normal or induced pH 5 enzymes. The microsomal system is also effective in catalyzing covalent binding of the nitroso compound with synthetic polyribonucleotides.

Animals↗
PubMed2000

A duplicated fold is the structural basis for polynucleotide phosphorylase catalytic activity, processivity, and regulation.

BACKGROUND: Polynucleotide phosphorylase (PNPase) is a polyribonucleotide nucleotidyl transferase (E.C.2.7.7.8) that degrades mRNA in prokaryotes. Streptomyces antibioticus PNPase also assays as a guanosine 3'-diphosphate 5'-triphosphate (pppGpp) synthetase (E.C.2.7.6.5). It may function to coordinate changes in mRNA lifetimes with pppGpp levels during the Streptomyces lifecycle. RESULTS: The structure of S. antibioticus PNPase without bound RNA but with the phosphate analog tungstate bound at the PNPase catalytic sites was determined by X-ray crystallography and shows a trimeric multidomain protein with a central channel. The structural core has a novel duplicated architecture formed by association of two homologous domains. The tungstate derivative structure reveals the PNPase active site in the second of these core domains. Structure-based sequence analysis suggests that the pppGpp synthetase active site is located in the first core domain. CONCLUSIONS: This is the first structure of a PNPase and shows the structural basis for the trimer assembly, the arrangement of accessory RNA binding domains, and the likely catalytic residues of the PNPase active site. A possible function of the trimer channel is as a contribution to both the processivity of degradation and the regulation of PNPase action by RNA structural elements.

Amino Acid Sequence↗
PubMed1988

Base cleavage specificity of angiogenin with Saccharomyces cerevisiae and Escherichia coli 5S RNAs.

The base cleavage specificity of angiogenin toward naturally occurring polyribonucleotides has been determined by using rapid RNA sequencing technology. With 5S RNAs from Saccharomyces cerevisiae and Escherichia coli, angiogenin cleaves phosphodiester bonds exclusively at cytidylic or uridylic residues, preferably when the pyrimidines are followed by adenine. However, not all of the existent pyrimidine bonds in the 5S RNAs are cleaved, likely owing to elements of structure in the substrate. Despite the high degree of sequence homology between angiogenin and ribonuclease A (RNase A), which includes all three catalytic as well as substrate binding residues, the cleavage patterns with natural RNAs are unique to each enzyme. Angiogenin significantly hydrolyzes certain bonds that are not appreciably attacked by RNase A and vice versa. The different cleavage specificities of angiogenin and RNase A may account for the fact that the former is angiogenic while the latter is not.

Adenocarcinoma↗
PubMed1980

Ribonucleic acid synthesis in the myocardium of spontaneously hypertensive rats. Quantification of transcribing ribonucleic acid polymerases.

Cardiac hypertrophy accompanies the progressive rise in blood pressure in spontaneously hypertensive rats. The role of endogenous RNA polymerases in this process was examined in nuclei from isolated cardiac myocytes of 20-week-old spontaneously hypertensive rats and normotensive Wistar-Kyoto controls. Both template-engaged (involved in transcription) and free (loosely attached to endogenous template, transcribing only with exogenous templates) RNA polymerases were increased in spontaneously hypertensive rats. In addition, the ratio of RNA polymerases I/II was lower in the spontaneously hypertensive rats for both functional pools of the enzyme. Endogenous transcribing RNA polymerases were quantified by t.l.c. of RNA-hydrolysis products. Increased numbers of enzyme molecules were present in nuclei from spontaneously hypertensive rats, without appreciable change in the rate of polyribonucleotide-chain elongation. These results could not be explained by differences in the activities of contaminating phosphatases or ribonucleases, nor by changes in endogenous nucleoside pools or recoveries of labelled nucleosides. Enhanced myocardial RNA synthesis in the spontaneously hypertensive rats at the stage of established cardiac hypertrophy is associated with increased numbers of RNA polymerase molecules. This increase may, in turn, reflect altered chromatin structure, resulting in increased polymerase binding and/or chain initiation.

Animals↗
PubMed2000

Transcriptional and post-transcriptional control of polynucleotide phosphorylase during cold acclimation in Escherichia coli.

Polynucleotide phosphorylase (PNPase, polyribonucleotide nucleotidyltransferase, EC 2.7.7.8) is one of the cold shock-induced proteins in Escherichia coli and pnp, the gene encoding it, is essential for growth at low temperatures. We have analysed the expression of pnp upon cold shock and found a dramatic transient variation of pnp transcription profile: within the first hour after temperature downshift the amount of pnp transcripts detectable by Northern blotting increased more than 10-fold and new mRNA species that cover pnp and the downstream region, including the cold shock gene deaD, appeared; 2 h after temperature downshift the transcription profile reverted to a preshift-like pattern in a PNPase-independent manner. The higher amount of pnp transcripts appeared to be mainly due to an increased stability of the RNAs. The abundance of pnp transcripts was not paralleled by comparable variation of the protein: PNPase steadily increased about twofold during the first 3 h at low temperature, as determined both by Western blotting and enzymatic activity assay, suggesting that PNPase, unlike other known cold shock proteins, is not efficiently translated in the acclimation phase. In experiments aimed at assessing the role of PNPase in autogenous control during cold shock, we detected a Rho-dependent termination site within pnp. In the cold acclimation phase, termination at this site depended upon the presence of PNPase, suggesting that during cold shock pnp is autogenously regulated at the level of transcription elongation.

Acclimatization↗