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At least 307 records · Page 17Linked to original sources
PubMed1975

Rapid onset of hyporesponsiveness to interferon induction on re-exposure to polyribonucleotide.

Only doses of complexed polyriboinosinic: polyribocytidylic acids sufficient to induce interferon, stimulated hyporesponsiveness to re-induction in rabbit kidney cells. Results of experiments designed to delineate the earliest time of appearance of hyporesponsiveness suggested the time of onset was less than i h after the end of a i h exposure to the inducer. The duration of hyporesponsiveness was about 24 h. Interferon itself did not produce hyporesponsiveness. Hence hyporesponsiveness must be related to an event or a substance synthesized before interferon production. The best candidate is a control protein inhibiting interferon production which is rapidly synthesized following exposure to an inducer.

Animals↗
PubMed1975

The effects of thioketo substitution upon uracil-adenine interactions in polyribonucleotides. Synthesis and properties of the alternating polynucleotides poly(r(A-s2U)) and poly(r(A-s2s4U)).

The polynucleotides poly[r(A-s-2U)] and poly]r(A-s2s4U)] have been synthesized and characterized by nearest-neighbour analysis, sedimentation analysis as well as spectroscopic techniques. Absorption-temperature profile and absorption-pH profile of poly[r(A-s-2U)] did not reveal a structural transition between 10 and 95 degrees C even at low ionic strength, although a variety of properties indicated a helical structure of poly[r(A-s-2U)]: remarkable hyperchromicity of the absorption spectrum, circular dichroic spectrum displaying extrema of large amplitudes, resistance against hydrolysis by ribonuclease and interaction with ethidium bromide in a manner which is characteristic of helical polynucleotides. Our results show that interactions of the type A-s-2U and A-s-2s-4U do in fact exist in helical polynucleotides. The properties of poly]r(As-2U)] furthermore demonstrate the general stabilizing effect of 2-thioketopyrimidine bases in helical polynucleotides by virtue of vertical stacking interactions with neighbouring pyrimiding and purine bases.

Circular Dichroism↗
PubMed1969

[Interferon induction increased through chemical modification of a synthetic polyribonucleotide].

The alternating copolymer riboadenylic-ribouridylic acid gained asignificant increase in ability to stimulate interferon production (2-to 20-fold) and cellular resistance (100-to 10,000-fold) both in vitro and in vivo upon substitution of phosphate by thiophosphate groups. The resulting nucleotide analog was also 10 to 100 times less sensitive to degradation by pancreatic ribonuclease, as determined byresidual antiviral activity.

Animals↗
PubMed1971

Release of nuclear DNA template restrictions by specific polyribonucleotides.

Certain synthetic homo- and copolyribonucleotide polymers are capable of releasing the DNA template restriction of isolated nuclei of rat liver cells when assayed with an excess of or in the absence of exogenous DNA polymerase. The purine homopolyribonucleotides are far more effective than are the pyrimidine polymers.

Adenine Nucleotides↗
PubMed1971

Comparison of the effects of a synthetic polyribonucleotide with the effects of endotoxin on selected host responses.

An injection of a small dose (1 to 50 mug) of synthetic polyriboinosinic acid complexed with polyribocytidylic acid (poly I:poly C) inhibited the induction of tryptophan oxygenase by cortisone acetate; it induced tyrosine amino transferase, and it accelerated the loss of liver glycogen reserves. It also resulted in first a suppression followed by an activation of the reticuloendothelial system as judged by the rates of carbon clearance from blood. All of these responses are elicited by comparable doses of endotoxin. Pretreatment of mice with poly I:poly C did not, or only marginally, increased their nonspecific resistance to infection with several bacterial pathogens, and it failed to result in the development of tolerance to endotoxin, effects known to be produced by endotoxin when given under similar conditions.

Journal Article↗
PubMed1967

Physiology of rickettsiae. VI. Host-independent synthesis of polyribonucleotides by Coxiella burnetii.

Preparations of purified and disrupted suspensions of Coxiella burnetii are able to incorporate ribonucleotides into polymers in the presence of adenosine, guanosine, cytidine, and uridine triphosphates. Nucleotide incorporation requires the presence of all four ribonucleoside triphosphates. The reaction is enhanced by the addition of phosphoenolpyruvate and pyruvic kinase, and exogenous deoxyribonucleic acid, and is inhibited by deoxyribonuclease and actinomycin D. Incorporation is maximal between pH 7.0 and 8.0, and at 37 C. The synthesized polymer is relatively insensitive to deoxyribonuclease and is sensitive to ribonuclease and dilute alkaline hydrolysis. The data indicate the presence of an autonomous deoxyribonucleic acid-dependent ribonucleic acid polymerase in the rickettsial agent.

Coxiella↗
PubMed1974

Histones stimulate polyribonucleotide-directed polydeoxyribonucleotide synthesis by murine leukemia virus.

The rate of homoribopolymer-directed DNA synthesis by detergent-disrupted Moloney murine leukemia virus can be stimulated or inhibited by histone, depending on the ratio of histone to template. Of the fractions which can be separated from the whole histone, f1 causes both the greatest stimulation and the greatest inhibition. The effect of histone f1 is qualitatively similar whether the template is polyadenylate (poly A), polycytidylate, or polyuridylate, but the stimulation is greatest with poly A. The pattern of stimulation and inhibition differs, however, for a different polymerase; the DNA polymerase of Micrococcus luteus is inhibited by histone concentrations which stimulate the viral enzyme and stimulated by concentrations which inhibit the viral enzyme. For the viral enzyme, the optimum histone concentration is unaffected by changes in the virus or primer concentration; but it varies in proportion to the template concentration, suggesting that histone acts by combining stoichiometrically with the template. These data raise the possibility that a histone-like protein may participate in the synthesis of the provirus of RNA tumor viruses.

Animals↗