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At least 1,081 records · Page 60Linked to original sources
PubMed1997

The solution structure of the S1 RNA binding domain: a member of an ancient nucleic acid-binding fold.

The S1 domain, originally identified in ribosomal protein S1, is found in a large number of RNA-associated proteins. The structure of the S1 RNA-binding domain from the E. coli polynucleotide phosphorylase has been determined using NMR methods and consists of a five-stranded antiparallel beta barrel. Conserved residues on one face of the barrel and adjacent loops form the putative RNA-binding site. The structure of the S1 domain is very similar to that of cold shock protein, suggesting that they are both derived from an ancient nucleic acid-binding protein. Enhanced sequence searches reveal hitherto unidentified S1 domains in RNase E, RNase II, NusA, EMB-5, and other proteins.

Amino Acid Sequence↗
PubMed1987

Clinical, immunological, and virological effects of ampligen, a mismatched double-stranded RNA, in patients with AIDS or AIDS-related complex.

10 patients with the acquired immunodeficiency syndrome (AIDS), AIDS-related complex (ARC), or lymphadenopathy syndrome (LAS) were given 200-250 mg ampligen, a mismatched double-stranded (ds) RNA with in-vitro antiviral activity against human immunodeficiency virus (HIV), twice a week for up to 18 weeks, without side-effects or toxicity. In all 9 patients who were positive for HIV RNA in peripheral blood mononuclear cells before therapy, levels became undetectable between days 10 and 40 of the start of therapy. 6 of the 7 patients with ARC or LAS also showed a progressive reduction in HIV load as measured by co-culture assays. All 10 patients had augmentation of delayed-type hypersensitivity skin reactions. Other changes noted during ampligen therapy included an increase in or maintenance of numbers of helper-inducer T lymphocytes, improvements in HIV-related symptoms, rises in titre of neutralising antibodies against HIV, and restoration of proper functioning of the natural lymphocyte antiviral dsRNA-dependent (2'-5'-oligoadenylate/RNA-ase L) pathway. Thus, in the short term, ampligen seems to have the dual ability to restore immunological function and to control HIV replication.

AIDS-Related Complex↗
PubMed1987

Mismatched double-stranded RNA (ampligen) reduces concentration of zidovudine (azidothymidine) required for in-vitro inhibition of human immunodeficiency virus.

'Ampligen', a non-toxic, mismatched polymer of double-stranded RNA with antiviral and immunomodulatory activities reduced the concentration of zidovudine (azidothymidine, AZT; 'Retrovir', Wellcome) required for inhibitory activity against human immunodeficiency virus (HIV) in vitro. At the higher doses of AZT tested, the virustatic activity observed seemed to have a synergistic virustatic relation with ampligen. Thus, combined therapy with ampligen and AZT can be expected to be more beneficial than AZT alone to patients with the acquired immunodeficiency syndrome (AIDS) or AIDS-related complex since AZT regimens that seem to be clinically effective are associated with considerable toxicity.

Antiviral Agents↗
PubMed1997

Purification and characterization of a novel poly(U), poly(C) ribonuclease from Saccharomyces cerevisiae.

A new ribonuclease from Saccharomyces cerevisiae, specific for poly(U) and poly(C) substrate, was purified near to homogeneity by successive fractionation with DEAE-Sepharose, Heparin-Sepharose and CM-Sepharose chromatography. The purified molecule detected by SDS/polyacrylimide gel electrophoresis has a molecular mass of 29 kDa. The optimum pH for the enzyme activity is 5.5-7 and its isoelectric point is 7.5. The purified enzyme was able to degrade 26S, 18S and 5S rRNAs as well as mRNA obtained from in vitro transcription. No catalytic activity was observed when the RNase was incubated with tRNA and double stranded substrate. Our findings suggest that this novel RNase may play an important role in the processing of RNA in Saccharomyces cerevisiae.

Chromatography, Affinity↗
PubMed1999

mRNA degradation. A tale of poly(A) and multiprotein machines.

The Escherichia coli RNA degradosome is a multiprotein complex containing an endoribonuclease, polynucleotide phosphorylase and a DEAD-box RNA helicase. A related complex has been described in the spinach chloroplast. The exosome and the mtEXO complex have recently been described in yeast and it is likely that related complexes also exist in animal cells. This research suggests the widespread existence of sophisticated machines for the efficient degradation of messenger RNA. The DEAD-box helicase in the degradosome can unwind regions of RNA structure that interfere with 3'-5' degradation. The polyadenylation of RNA 3' ends is also known to promote degradation by creating a 'toehold' for the degradation machinery. Much remains to be learned about the regulation of mRNA stability. The complexity of the degradation process, both in the eubacteria and in the eukaryotes, suggests that many steps are possible points of control.

Bacterial Proteins↗
PubMed1975

[Analysis of a small quatity of polypeptides by two-dimensional electrophoresis: application to characterization of proteins].

A new two-dimensional electrophoresis is described. The first electrophoresis is performed in a 10 p. cent gel (1 X 110 mm) in the presence of 7 M urea; the migration in the second dimension proceeds on a 20 p. cent polyacrylamide sheet (160 X 110 X 1 mm) in the presence of sodium dodecyl sulphate. This system resolves most of the polypeptides obtained by treating a very small amount (about 100 mug) of proteins with cyanogene bromide. Macromolecules can thus be quickly and easily characterized.

Alkaline Phosphatase↗
PubMed1975

[Quaternary structure of Escherichia coli polynucleotide phosphorylase: chemical characterization of form A].

We had previously shown the existence of two classes of polynucleotide phosphorylases : Form A which is made of alpha chains and carries the catalytic sites ; and form B which is constituted of alpha chains and of beta chains. We performed some chemical analyses of form A (N-terminal sequence, amino acid composition, peptide mapping) which suggest that the alpha chains are all identical and moreover that they have no relationship with the beta chains. The latter do not therefore derive from a partial proteolytic degradation of the alpha chains and can therefore be considered as true subunits of the enzyme.

Amino Acid Sequence↗
PubMed1976

A comparative study by sucrose gradient electrophoresis of messenger ribonucleoprotein complexes.

The recently developed method of sucrose gradient electrophoresis has been used in the investigation of mRNA containing particles prepared in an undenatured state. The particles containing messenger RNA migrate as a homogeneous fraction with a mobility different from that of ribosomal praticles. Informosomes and polysomal mRNPs have about the same mobility. On the contrary artificial complexes, formed by the reaction of cytoplasmic binding factor with RNA, migrate as a heterogeneous fraction. The particles carrying mRNA are drastically and irreversibly affected by a treatment with EDTA. Sodium deoxycholate removes some proteins but seems also to denature them. After treatment by high salt or Sodium deoxycholate the mRNPs migrate as a homogeneous fraction showing that all particles are equally affected.

Electrophoresis↗
PubMed1978

[Quaternary structure and proteolysis of the polynucleotide phosphorylase from C. perfringens].

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.

Chemical Fractionation↗
PubMedDate not supplied

Mutagenesis by alkylating agents: coding properties for DNA polymerase of poly (dC) template containing 3-methylcytosine.

After treatment of poly(dC) by the simple alkylating agent (3H)dimethylsulfate, 90 per cent of the radioactivity cochromatographied with 3-methylcytosine and 10 per cent with 5-methylcytosine which is the normally occurring methylated base. In order to study the influence of 3-methylcytosine on DNA replication, untreated and DMS-treated poly(dC) were used as templates for E. coli DNA polymerase I. The alkylation of poly(dC) inhibits DNA chain elongation, and does not induce any mispairing under high fidelity conditions. The alteration of DNA polymerase I fidelity by manganese ions allows some replication of 3-methylcytosine which mispairs with either dAMP or dTMP. Our results suggest that 3-methylcytosine could be responsible, at least partially, for the killing and the mutagenesis observed after cell treatment by alkylating agents.

Alkylating Agents↗
PubMedDate not supplied

Template properties of ultraviolet-irradiated poly(dC) replicated by E. coli DNA polymerase I: indication for a role of apyrimidinic-sites in UV-induced mutagenesis.

Ultraviolet irradiation alters the template properties of poly(dC) when replicated by Escherichia coli DNA polymerase I. These effects are due to base modifications. Some of them are identified as apurinic/apyrimidinic sites (AP-sites) by their sensitivity to AP-endonuclease B purified from Micrococcus luteus, and their template properties. The rate of formation of AP-sites in poly(dC) is estimated at 3 X 10(-7) site per nucleotide per J.m-2. Exposure of supercoiled or relaxed pBR322 DNA to UV light results also in the formation of sites sensitive to AP-endonuclease B. In this case, the rate of formation of AP-sites is the same in relaxed or supercoiled DNA: 0.3 X 10(-7) site per nucleotide per J.m-2. The apyrimidinic sites are generated through the processing of an ultraviolet induced primary lesion. We suggest that this lesion is cytosine hydrate by its rate of decay and preferential formation in single stranded DNA. Our results suggest that AP-sites might be a minor pathway leading to UV-induced mutagenesis.

Cytosine↗