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At least 721 records · Page 40Linked to original sources
PubMed1995

Double-stranded RNA: the variables controlling its degradation by RNases.

The kinetics of single-stranded (SS) and double-stranded (ds) polyribonucleotides cleavage by three mammalian pancreatic type ribonucleases have been studied under low and high salt conditions. The values kcat, Km, and kcat/Km for depolymerization of poly(U), poly(A).poly(U), poly(I) and poly(I).poly(C) by bovine RNase A, bovine seminal RNase, and human seminal RNase have been determined and compared to each other. The Km values of bovine RNase A for (ss) or (ds) substrates were of the same order of magnitude under low and high ionic strength conditions, while their kcat values were found to differ considerably. Qualitatively similar results were obtained with bovine and human seminal RNases, i.e., the activity ratios (ssRNA/dsRNA) were mostly determined by the ratio of kcat values. It was shown that the modest levels of activity toward dsRNAs shown by single-strand-preferring RNases may occur by a mechanism consisting in the binding of the RNase to single nucleotides which are wound off the double helix because of thermal fluctuations. A higher activity and its enhancement as a function of number and location of the positive charges present on the RNase surface (human seminal RNase > bovine seminal RNase > bovine RNase A), as well as its increase under low ionic strength conditions, could instead be explained by the increased occurence of the splitting mechanism based on the binding of the RNase to single-stranded RNA sequences transiently exposed from the RNA double-helix.

Animals↗
PubMedDate not supplied

[Production of type I interferons in the body exposed to yeast RNA-tiloron molecular complexes].

Molecular complexes forming as a result of interaction between yeast RNA preparations with 2,7-bis[-(diethylaminoethoxy)-fluorene]-9-on dihydrochloride (tilorone) administered parenterally to mice cause the appearance of interferon in high titers compatible to those induced by standard inductors of polyribonucleotide origin, poly(I)-poly(C) and larifan. Some physiologic conditions of interferonogenesis have been studied. The above molecular complexes in the dose range used experimentally were completely nontoxic. Hence, these complexes are promising agents for interferon induction.

Animals↗
PubMedDate not supplied

[The passive transfer by Drosophila spermatozoa of exogenous DNA molecules or synthetic polynucleotides into fertilizable eggs].

Experiments on mutation induction in Drosophila melanogaster by injections of exogenous DNAs or a synthetic polyribonucleotide solutions into the hemolymph of the male demonstrated that Drosophila spermatozoa were able to transfer passively molecules of these mutagens into fertilized eggs. This induced mutations in both paternal and maternal chromosomes in offspring.

Animals↗
PubMed1977

An in vitro study on the interaction between dimethylnitrosamine and nucleic acids via a microsomal system.

Radioactive alkylated bases, ribose or phosphate, were never found either in acid and alkaline hydrolysates of polyribonucleotides or in alkaline hydrolysates of DNA after incubation with 14C-dimethylnitrosamine (DMNA) in a microsomal system. Two radioactive compounds, which were co-chromatographed with methylamine and N-methylhydrazine, respectively, on column, paper, and thin-layer, were always detected. They differed from the compound derived from 7-methylguanosine after the alkali-mediated fission of the imidazole ring in its molecule. The in vitro system employed well represents the in vivo situation (7-methylguanine which is liberated from DNA after acid hydrolysis); however, it has given results which do not agree with the generally-accepted mechanism of DMNA alkylation at the N-7 position of guanine.

Animals↗
PubMed1977

Purification and mode of action of exoribonuclease from bovine brain.

The exoribonuclease in bovine brain has been purified about 900-fold in 10% yield. The molecular weight is about 65,000. The enzyme is free from other ribonucleases of bovine brain. Studies of the mode of action of the enzyme show the following: (a) The enzyme cleaves both oligo- and polyribonucleotides exonucleolytically, initiating nucleolytic attack from the 5'-hydroxyl end to yield 3'-mononucleotides. The enzyme differs from spleen exonuclease in that it does not act on polydeoxyribonucleotides. (b) When the 5'-hydroxyl group is phosphorylated, the enzyme is inactive. (c) The enzymic action is processive in nature; the enzyme hydrolyzes one polynucleotide chain to completion before proceeding to the degradation of another chain.

Animals↗
PubMedDate not supplied

[Effect of interferon inducers on the development of specific resistance to tick-borne encephalitis].

Various natural and synthetic interferon inducers stimulate postvaccination immunity to tick-borne encephalitis virus in mice. This capacity was found not only in macromolecular synthetic polyribonucleotides such as (poly I)-(poly C), (poly G)-(poly C), (poly A)-(poly U) and substances with much lower molecular weight such as copolymers of vinylpyrrolidone with maleic anhydride, crotonic acid or metacrylic acid but also in a low molecular interferon inducer tiloron. These and other interferon inducers examined (endotoxin S-typhi, statolon) exhibited no parallelism between the intensity of their stimulating effect of immunogenesis and levels of interferon production induced in mice and the associated resistance to tick-borne encephalitis. The results indicate a possibliity of using various interferon inducers for stimulation of post-vaccination immunity to tick-borne encephalitis.

Animals↗
PubMed1976

[Antiviral activity of a poly A-poly U complex administered by various routes].

Interferon-inducing and antiviral activity of a synthetic polyribonucleotide, polyaenylic and polyuridylic acid complex (poly A--poly U) was studied comparatively on a model of experimental infection of albino mice caused by Venezuela Horse Encephalomyeliti Viruos (VHEV) using oral and intraperitoneal administration of the complex. It was shown that dm-interferon induction and antiviral effect comparatively high doses of poly A--poly U (Reanal) were required (1 mg/mouse). The highest antiviral effect was observed after a two-fold administration of the drug (24 hours and immediately before infection). It was more evident after intraperitoneal administration of the inductor. The interferon titers in the animal blood serum after intraperitoneal or oral administration of poly A--poly U were almost the same 58=60+/- +/- 18.9 IU50/ml).

Administration, Oral↗
PubMed1976

Modification of the 5' terminus of mRNA by an RNA (guanine-7-)-methyltransferase from HeLa cells.

The 5' termini of many viral and cellular mRNAs contain sequences of the type m7G(5")pppNm. An RNA (guanine-7-)-methyltransferase that specifically methylates the 5'-terminal guanosine residue of RNAs ending in the dinucleoside triphosphate G(5')pppN- has been purified from the cytoplasm of HeLa cells. Approximately two-thirds of the methyltransferase activity detected in an assay employing umnethylated vaccinia virus mRNA as acceptor was located in the cytoplasm when cells were disrupted by Dounce homogenization; 30% of the cytoplasmic activity was associated with ribosomes but was removed by washing with 0.5 M KCl. The enzyme was purified 165-fold from the cytoplasm by removing nucleic acid by phase partition followed by ammonium sulfate precipitation and column chromatography on DEAE-cellulose, denatured DNA-agarose, and CM-Sephadex. The partially purified enzyme preparation methylated heterologous tRNAs as well as vaccinia mRNA, but the tRNA methyltransferases could be separated from the mRNA activity by sucrose gradient sedimentation and gel filtration on Sephadex G-200. The product of the partially purified enzyme using vaccinia mRNA as substrate was exclusively 7-methylguanosine located in the terminal dinucleoside triphosphate. In addition to RNAs and synthetic polyribonucleotides terminating in a dinucleoside triphosphate, free G(5')pppG could be methylated but GTP, GDP, and G(5')pppG could not. The enzyme also methylated the dinucleoside diphosphate G(5')pppG but much less efficiently than G(5')pppG. An S20, W of 3.8, a Stokes radius of 3.6 nm, and a molecular weight of 56,000 were obtained from sucrose gradient sedimentation and Sephadex G-200 column chromatography.

Base Sequence↗
PubMed1978

Polynucleotides. XLIV. Synthesis and properties of poly (2-azaadenylic acid) and poly(2-azainosinic acid).

Chemically synthesized 2-azaadenosine 5'-diphosphate (n2ADP) and 2-azainosine 5'-diphosphate (n2IDP) were polymerized to yield poly(2-azaadenylic acid), poly(n2A), and poly(2-azainosinic acid), poly(n2I), using Escherichia coli polynucleotide phosphorylase. In neutral solution, poly(n2A) and poly(n2I) had hypochromicities of 32 and 5.5%, respectively. Poly(n2A) formed an ordered structure, which had a melting temperature (Rm) of 20 degrees C at 0.15 M salt concentration. Upon mixing with poly(U), poly(n2A) formed a 1 : 2 complex with Tm of 41 degrees C at 0.15 M salt concentration. Poly(n2A) and poly(n2I) formed three-stranded complexes with poly(I), and poly(A), respectively. Poly(n2A) . 2poly(I), poly(A) . 2poly(n2I), and poly(n2A) . 2poly(n2I) complexes had Tm values of 23, 48, and 31 degrees C at 0.15 M salt concentration, respectively. Poly(n2I) formed a double-stranded complex with poly(C), but its Tm was very low.

Circular Dichroism↗
PubMed1979

Poly(2-fluoroadenylic acid). The role of basicity in the stabilization of complementary helices.

The polymerization of 2-fluoroadenosine 5'-diphosphate by polynucleotide phosphorylase to give high molecular weight poly(2-fluoroadenylic acid), poly(fl2A), is described. Both the single-stranded and double-stranded (acid) forms of poly(fl2A) exhibit strikingly similar ultraviolet and circular dichroism spectra to those of poly(A), and the enzymatic polymerization rates and thermal hyperchromicities of the two polymers are also very similar. However, the pKa of poly(fl2A) for protonation at N-1 is 2.9 compared to 5.9 for poly(A) under similar conditions. Poly(fl2A) forms a triple-stranded helix with poly(U) which has ultraviolet and cd spectra very reminiscent of poly(A) . 2 poly(U), but no conditions could be found which permitted the formation of a double helix. In the Escherichia coli ribosome system poly(fl2A) codes for the synthesis of polylysine, as does poly(A), although the rate and extent of incorporation were less in the former case. The role of basicity of adenine N-1 in these interactions is discussed.

Drug Stability↗
PubMed1982

Poly(7-deazaguanylic acid), the homopolynucleotide of the parent nucleoside of queuosine.

Poly(7-deazaguanylic acid) was enzymatically synthesized by the polymerization of 7-deazaguanosine 5'-diphosphate with polynucleotide phosphorylase from Micrococcus luteus in high yield. The homopolymer showed a similar thermal and total hypochromicity to poly(G) at the long wavelength absorption maximum. No sigmoid melting profile was observed for poly(c7G) as is found for poly(G), implying a single-stranded structure in aqueous solution. From the circular dichroism spectra it can be concluded that the 7-deazapurine nucleotide is much more flexible than the purine nucleotide. In analogy to poly(G), the homopolymer poly(c7G) forms a 1:1 complex with poly(C) under neutral conditions, melting at a similar temperature to the poly(G) complex. However, at pH 2.5, where a poly(G) X 2poly(C) complex is observed, poly(c7G) still binds only one poly(C) strand. This is due to the lack of N-7 in poly(c7G), not allowing Hoogsteen base pair formation, which occurs with poly(G). RNase T1 cleaves poly(c7G), indicating that N-7 of guanosine is not a requirement for nucleotide binding to the enzyme, as has been suggested. Because of the single-stranded structure of poly(c7G), the polynucleotide chain is rapidly hydrolyzed by the single-strand-specific nuclease S1, whereas multistranded poly(G) is completely resistant.

Base Composition↗
PubMed1975

Poly(8-aminoguanylic acid): formation of ordered self-structures and interaction with poly(cytidylic acid).

Poly(8-aminoguanylic acid) has in neutral solution a novel ordered structure of high stability. The 8-amino group permits formation of three hydrogen bonds between two residues along the "top", or long axis, of the purines. The usual hydrogen bonding protons and Watson-Crick pairing sites are not involved in the association. The bonding scheme has a twofold rotation axis and is hemiprotonated at N(7). Poly(8NH2G) is converted by alkaline titration (pK = 9.7) to a quite different ordered structure, which is the favored form over the range approximately pH 10-11. The bonding scheme appears to be composed of a planar, tetrameric array of guanine residues, in which the 8-amino group does not participate in interbase hydrogen bonding. Poly (8NH2G) does not interact with poly(C) in neutral solution because of the high stability of the hemiprotonated G-G self-structure. Titration to the alkaline plateau, however, permits ready formation of a two-stranded Watson-Crick helix. In contrast to the monomer 8NH2GMP, poly(8NH2G) does not form a triple helix with poly(C) under any conditions. The properties of the ordered structures are interpreted in terms of a strong tendency of the 8-amino group to form a third interbase hydrogen bond, when this possibility is not prevented by high pH.

Binding Sites↗
PubMed1983

Poly(2-methylthio-7-deazainosinic acid)--hydrophobic stabilization of polynucleotide secondary structure by the 2-methylthio group.

Poly(2-methylthio-7-deazainosinic acid) [poly(ms2c7I)] was enzymatically synthesized by polymerization of 2-methylthio-7-deazainosine 5'-diphosphate with polynucleotide phosphorylase from Micrococcus luteus in high yield. The homopolymer shows much higher thermal stability than its parent polynucleotides poly(7-deazainosinic acid) [poly(c7I)] and poly(I). Its sigmoidal melting curve and pronounced hypochromicity imply a rigid, ordered structure. Poly(ms2c7I), like poly(2-methylthio-inosinic acid) [poly(ms2I)], does not form a complex with poly(C) because of the bulky 2-methylthio substituent. On the other hand, two poly(ms2c7I) strands form very rigid triple strands with poly(A). Different from poly(I) and poly(c7I) the homopolymer poly(ms2c7I) is very stable against cleavage by nuclease S1 and ribonuclease T2 as expected from its rigid secondary structure.

Circular Dichroism↗
PubMed1976

Polynucleotides. XLII1. Limited addition of 2'O-onitrobenzyl nucleotides to the 3'-end of ribooligonucleotide with polynucleotide phosphorylase.

2'-O-o-Nitrobenzyluridine, -cytidine and -adenosine were phosphorylated with phosphoryl chloride to the corresponding 5'-phosphates and led to 5'-diphosphates by the method of Moffatt and Khorana. These 2'-O-oNB-nucleoside 5'-diphosphates were incubated with a primer CpApA and polynucleotide phosphorylase in the presence of Mn2+. Tetranucleotides CpApApU, CpApApC and CpApApA were obtained after photosensitive removal of oNB groups in yields of 54-70%.

Benzyl Compounds↗