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At least 19 recordsLinked to original sources
PubMed1977

Rupture of base pairing in double-stranded poly(riboadenylic acid)-poly(ribouridylic acid) by formaldehyde: medium chain lenghts.

By assuming that the opening of hydrogen bonds due to thermal fluctuations is a very fast step and that the reaction of formaldehyde with the imino or amino group is a slow step, we have constructed a model for the unwinding process of poly(A-U) induced by formaldehyde. The denaturation equation derived from the model is essentially the same as that of the zipper model for moderately long chain lengths. The model predicts the following phenomena which are in agreement with our experimental findings. The rate of unwinding is approximately first order for unfractionated polynucleotides and zero order for fractionated samples. This means that formaldehyde ruptures helical residues sequentially starting from the ends and working toward the center. Our model further predicts that the denaturation rate is linearly dependent on -log[Na+] and pH at low ionic strength and is almost independent of [Na+] and pH at high ionic strength. Spectrophotometric measurements on poly(A-U) were done to confirm our theoretical findings.

Chemical Phenomena↗
PubMed1976

Platinum binds selectively to phosphorothioate groups in mono- and polynucleotides: a general method for heavy metal staining of specific nucleotides.

Platinum binding to nucleoside phosphorothioates has been examined to determine their suitability as heavy metal labeling sites for the potential electron microscopic sequencing of nucleic acids. The complex platinum terpyridine nitrate forms a 1:1 adduct with either adenosine or uridine monophosphorothioate. Spectroscopic evidence strongly indicates the presence of platinum-sulfur bonds. Both platinum terpyridine nitrate and chloroterpyridineplatinum(II) bind to poly(sA-U), a polymer prepared from adenosine 5'-O-(1-thiotriphosphate) and UTP. Binding to the sulfur atoms of the phosphorothioate groups is quantitative, as shown by double label experiments using [35S]poly(sA-U) and [3H]chloroterpyridine-platinum(II). Similar experiments with [14C]poly(A-U) indicated no platinum binding. No evidence of nicking or loss of sulfur from poly(sA-U) could be detected after platinum binding. The phosphorothioate group is a strong, highly selective binding site for platinum in polynucleotides. Previous studies have demonstrated quantitative enzymatic incorporation of phosphorothioate groups into a polynucleotide adjacent to a specific base [Matzura, H. & Eckstein, F. (1968) Eur. J. Biochem. 3, 448-452]. The use of heavy metal-labeled phosphorothioate groups for the sequencing of nucleic acids by electron microscopy therefore appears feasible.

Adenosine Triphosphate↗
PubMed1978

Study on plant RNAases. Isolation and properties of several activities from Vicia faba root cells.

Vicia faba root cells contain several nucleolytic activities: phosphomonoesterase and phosphodiesterase (which however were not studied in details), one nuclease and four ribonucleases. These results were obtained by separating the extracted proteins into anionic and cationic species by chromatography on CM-cellulose at pH 5.5 and analysing each kind of proteins. Anionic species were subjected to chromatography on DEAE-cellulose which lead to isolation of one nuclease (A1) and two RNAases (A2, A3), the properties of which were studied. It was shown that the RNAases pH optima are near 6; A2 is more thermolabile than A3; both are endonucleases unable to attack double-stranded structure; studies with homopolymers, i.e. poly(A), poly(I), poly(C), poly(U), showed that their base specificities were analogous to that of already known plant RNAases. The cationic proteins, analysed with CM-cellulose, contain two RNAases (C1, C2). The pH optima were near 6 and 7, respectively; C1 is much more thermolabile than C2; both were endonucleases inactive on double-stranded structures. C1 and C2 hydrolysed poly(C) and poly(U) but not poly(A) and poly(U).

Cations↗
PubMed1975

Structural features of double-stranded polyribonucleotides required for immunological specificity and interferon induction.

Purified antibody to poly(adenylic acid)-poly(uridylic acid) was used in quantitative microcomplement fixation assays to detect conformational variations among several double-helical polyribonucleotide analogs of poly(adenylic acid)-poly(uridylic acid) or poly(inosinic acid)-poly(cytidylic acid) that had been previously evaluated for their ability to induce interferon. Modification at the furanose 2'-position of one or both strands resulted in a dramatic decrease in serological reactivity. Most modifications of the bases caused smaller serological changes, and no base modification caused complete loss of reactivity. The reaction patterns support the conclusion that the structure of the furanose and the overall conformation of the helix are critical in the formation of antigenic determinants. The backbones of both strands appear to be involved in forming a single antigenic site, and base modifications may alter the steric relationship between the backbones. In addition, the same structural changes that substantially alter recognition by antibody also lead to large changes in the interferon-inducing ability of the nucleic acid.

Antigen-Antibody Reactions↗
PubMed1976

Interferon: effects on the immune response and the mechanism of activation of the cellular response.

The discovery of interferon in 1957 by Drs. Isaacs and Lindenmann led to major revisions in the concepts of man's defenses against viral infections. There are at least two types of interferon. Along with their antiviral properties, they have recently been shown to exert a suppressive effect on the humoral and cellular immune response; they affect both B and T lymphocytes. A variety of substances, including virus, polyribonucleotides, and mitogens for T lymphocytes, are good interferon inducers. T lymphocytes seem to be necessary for these inducers to exert their immunosuppressive effects. The immunosuppressive effects of interferon inducers suggests that interferons may be mediators of suppressor T lymphocyte effects. In the virus system, interferon does not exert its antiviral effects by direct action on the virus, but rather derepresses a cell gene that results in the production of an antiviral protein. This antiviral protein is probably the mediator of inhibition of virus replication. This is a complex sequence of events that results in the interaction of interferon with the cell membrane and the resulting production of the antiviral state in the cell. This review will examine the various steps of this involved process.

Animals↗
PubMed1975

Immunochemical characterization of the anti-RNA antibodies found in scleroderma and systemic lupus erythematosus. I. Differences in reactivity with Poly (U) and Poly-(A) Poly (U).

In a previous study, all 40 sera from patients with scleroderma, 20 of 40 sera from SLE patients, but none of 40 sera from normal controls, were found to have antibodies to ssRNA. All scleroderma sera were also found to react with HSA-coupled uridine and UMP and their reaction with HSA-coupled uridine and UMP and their reaction with ssRNA could be inhibited by uracil, uridine, and UMP. To characterize further these uracil-specific anti-RNA antibodies found in scleroderma and compare them with the anti-RNA antibodies found in SLE, we tested their reactivity with Poly (U) and with Poly (A)-Poly (U) and all but one failed to react with Poly (A)-Poly (U). This same serum was the only one in which the reaction with Poly (U) could not be inhibited with uracil. Reactivity of SLE sera was strikingly different from that found in scleroderma sera. Seventeen of 34 SLE sera studied reacted with ssRNA but only four of these reacted with Poly (U). Conversely, two SLE sera that reacted with Poly (U) did not react with ssRNA. Fifteen reacted with Poly (A)-Poly (U) and only two of these failed to react with ssRNA. Five SLE sera which were reactive with ssRNA did not precipitate with Poly (A)-Poly (U). All SLE sera which reacted with Poly (U) could be inhibited with uracil, although less effectively than in scleroderma. Reactivity with Poly (A)-Poly )U) was not inhibited with uracil nor with adenosine. These findings confirm that antibodies to RNA that are found in scleroderma are directed to uracil and thus specific to ssRNA, whereas RNA antibodies found in SLE sera are heterogeneous and directed to either the base, to the site of union of the base and sugar moiety to the ribose backbone, or to the helical structure of double stranded RNA. These differences and the respective antigenic specificities of these anti-RNA antibodies found in scleroderma and SLE may be theoretically important.

Adenine↗
PubMed1978

[Immunostimulation].

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Adjuvants, Immunologic↗
PubMed1975

Molecular basis of chromosome banding. II. The effect of silver and mercury ions on the fluorescence intensity of acranil-DNA complexes.

Silver and mercury ions are known to react with the bases of nucleic acids in solution. At low cation/base ratios Ag+ has an affinity for GC pairs in DNA, whereas Hg++ is preferentially bound to AT-rich nucleic acids. We have used fluorometry to measure the effect of these cations on the fluorescence intensity of preformed complexes of acranil and DNA in solution. The results are: 1) Ag+ enhances the fluorescence intensity presumably by affecting the dye intercalated in the vicinity of GC-pairs. 2) The addition of Hg++ leads to a quenching of the fluorescence intensity of the complex at low ion/base ratios, suggesting an effect on the dye molecules bound to AT pairs. At high GC-content of the nucleic acid, slight enhancement of the fluorescence intensity occurs with Hg++. 3) With both metals there is a correlation between base content of DNA and effect on the intensity of fluorescence indicating base specificity of the dye-polymer interaction.

Acridines↗
PubMed1976

Binding of ampholine to transfer RNA.

The melting temperature of isoaccepting tRNAfMet is affected by Ampholine. The plot of Tm versus the logarithm of Ampholine concentration shows clearly an increasing effect of Ampholine when the pH changes from 7.4 to 4.2. This result is interpreted as binding of Ampholine to the nucleic acid. The effects of Ampholine have been compared with those of soidum, magnesium and tetraethylene pentamine. Ampholine carrier ampholytes at pH 4.2 bind to tRNA with the same affinity as magnesium; at higher pH values they are less active. An hypothesis for the mechanism of action of Ampholine on nucleic acids during isoelectric focusing is proposed.

Bis-Trimethylammonium Compounds↗
PubMed1978

Antibodies to synthetic polyribonucleotides in spouses of patients with inflammatory bowel disease.

Serum from patients with inflammatory bowel disease (I.B.D.) and their unaffected spouses bound significantly more synthetic single-stranded (poly.rA) and double-stranded (poly.rA.poly.rU) R.N.A. but not KB cell D.N.A. than did serum from age-matched controls and their spouses. Binding activity resided in Ig fractions and was predominantly of IgM class. A significant corelation was observed between the amount of double-stranded but not single-stranded R.N.A. bound by serum from patients and from their respective spouses. These findings provide indirect support for the presence of R.N.A. viruses in patients with I.B.D. and the transmission of such agents to their close personal contacts.

Antibodies, Viral↗
PubMed1975

Factors influencing activation of B-cells in immunity.

The hypotheses so far advanced for B-cell activation by antigen are based on the assumption that the interaction between antigen and the Ig receptors delivers at least the initial triggering signal. There are few, if any, experimental findings to support this assumption. On the contrary, a variety of findings indicate that the Ig receptors do not deliver any signal to the cells, whereas activation can be regularly achieved without participation ofIg receptors. The available evidence forces us to suggest that antigen-induced B-cell triggering is always caused by one nonspecific signal, which is delivered to the cells by surface structures, which are not the Ig receptors. For distinctive features of this hypothesis see One Nonspecific Triggering Signal. Various competing hypotheses for B-cell activation have been analyzed, but none of them appears to satisfy the experimental findings.

Animals↗
PubMed1975

Acceleration of autoimmunity in NZB/NZW F1 mice by graft-versus-host disease.

Chronic graft-versus-host (GVH) disease was induced in NZB/NZW F1 (B/W) hybrid female mice by the weekly injection of parental NZB spleen cells. Control mice received injections of syngeneic spleen cells only. The mice were assayed for antibodies to [3H]DNA and [3H]polyadenylic-polyuridylic acid by a cellulose ester filter radioimmunoassay, and for antibody to thymocytes by a cytotoxicity method. GVH disease accelerated the development of all three antibodies in B/W mice. In addition, sucrose density gradient ultracentrifugation of pooled sera suggested that an accelerated switch from 19S to 7S anti-DNA production may be an early effect of GVH. The mechanism of acceleration is discussed in terms of immunological and viral factors generated by the GVH reaction.

Animals↗