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Query: HUMANGGP:021254 (ribonucleoprotein)
 6,852 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. The specific activity of rat and pig liver nuclear-envelope nucleoside triphosphatase (EC 3.6.1.3) decreases when the system is depleted of RNA. The activity can be restored by adding high concentrations of yeast RNA to the assay medium. 2. Exogenous RNA also increases the activity of the enzyme in control envelopes (not RNA-depleted). The effect appears to be largely specific for poly(A) and poly(G); it is not stimulated by rRNA or tRNA preparations, ribonuclease-hydrolysed RNA, AMP, or double- or single-stranded DNA. 3. Inhibitors of the enzyme, in concentrations at which half-maximal inhibition of the enzyme is achieved, do not affect the percentage stimulation of the enzyme by yeast RNA. 4. The simulation is abolished by the inclusion of 150 mM-KCl or -NaCl in the assay medium, but not by increasing the assay pH to 8.5. 5. The results are discussed in the light of the possible role of the nucleoside triphosphatase in vivo in nucleo-cytoplasmic ribonucleoprotein translocation. 6. It is proposed that poly(G)-stimulated Mg2+-activated adenosine triphosphatase activity should be adopted as an enzymic marker for the nuclear envelope.
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PMID:Ribonucleic acid stimulation of mammalian liver nuclear-envelope nucleoside triphosphatase. A possible enzymic marker for the nuclear envelope. 14 Dec 76

Small stable RNA molecules of Escherichia coli other than 5S (rRNA) and 4S (tRNA) were studied. Two of the molecules corresponded to 4.5S and 6S RNA, which have been reported previously. The third stable RNA molecule, 10S RNA, has not been described before. RNA labeled with (32)P(i) or [(14)C]uracil for a relatively long time, when separated in 5%/12% tandem polyacrylamide gels, displayed three bands corresponding to 10S, 6S, and 4.5S RNA in addition to rRNA and tRNA bands. These RNAs were stable in pulse-chase-labeling experiments. The amount of these RNAs was small, comprising only 0.2 to 0.5% of the total (32)P incorporation. However, this amount represented a large number of molecules; for 6S and 4.5S, it was about 1,000/DNA molecule. These three RNAs were found in the postribosomal supernatant fraction. None of them was found in purified nucleoid fractions in which the tightly coiled DNA molecules were contained. Of these three RNAs, 6S RNA was unique in that it seemed to exist in a ribonucleoprotein particle. All these RNAs, as well as tRNA, were very stable in the cell under various physiological conditions. 5S RNA was less stable. On the other hand, purified 6S RNA was more susceptible than tRNA to cell nucleases when incubated with cell extracts, suggesting that, being in a particle, it is protected from cell nucleases.
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PMID:Small stable RNAs from Escherichia coli: evidence for the existence of new molecules and for a new ribonucleoprotein particle containing 6S RNA. 34 86

Native small ribosomal subunits in mouse ascites tumor cells prepared by a sucrose zone sedimentation and analyzed by CsCl isopycnic centrifugation, consisted of four kinds of particles which could be distinguished reproducibly by their ultraviolet absorption. These particles had buoyant densities at 1.40, 1.42, 1.46 and 1.49 g/cm3 and were designated as S1, S2, S3 and S4 particles respectively. Studies on labeling kinetics with radioactive RNA precursors and the pulse label--actinomycin D chase experiment, demonstrated that radioactivity was incorporated first in precursor particles with a density of 1.45 g/cm3 and then appeared in S3, S1 and/or S2 and S4 particles. Results on labeling after administration of actinomycin D and EDTA treatment of the labeled small subunits revealed that S1 and S2 particles contained a messenger-like ribonucleoprotein particle and this particle plus tRNA, respectively. Since appearance of newly formed S4 particle was remarkably delayed and the amount of it was reduced after incubation of the cells in vitro with 10 mM sodium fluoride, this particle originated from dissociation of the small subunit.
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PMID:Properties and synthesis of multiple components in native small ribosomal subunits of mouse ascites tumor cells. 80 41

By means of affinity chromatography on poly(adenylic acid) (poly(A))-fixed Sepharose, protein fractions having strong affinity to poly(A) were prepared from postribosomal supernatants of rabbit reticulocyte and rat liver. These fractions contained several proteins similar by electrophoretic analysis to rabbit globin messenger ribonucleoprotein. Protein fractions from both sources were shown to form ribonucleoprotein complexes with rabbit globin mRNA, and these complexes sedimented at the same rate as native globin messenger ribonucleoprotein. Binding of the proteins to RNA was not highly specific, since not only poly(A) but also other polynucleotides as poly(C) or poly(U) were bound to these proteins. Ribosomal RNAs, tRNA, or DNAs did not bind the proteins. In order to ascertain the function of the poly(A)-Sepharose purified proteins, their effects on translation of globin mRNA was studied in vitro. Addition of rabbit reticulocyte protein to globin mRNA resulted in no more than a slight stimulation of both alpha- and beta-chain synthesis. Poly(A)-Sepharose purified protein from rat liver, however, caused a marked preferential reduction of alpha-chain synthesis. These results showed that at least some proteins in the poly(A)-Sepharose purified proteins affect the translation of globin. This inference suggested a possibility that protein moiety in globin mRNP might be involved in control of globin synthesis.
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PMID:In vitro translation of globin: effect of proteins purified by affinity chromatography on polyadenylate-Sepharose. 95 76

Messenger ribonucleoprotein particles (mRNPs) have been isolated from rabbit reticulocyte polysomes. One of the proteins of the mRNP complex has many properties of a specific eukaryotic initiation factor, the soluble Met-tRNA-f binding protein. A purified preparation of this factor, in addition to binding Met-tRNA-f, binds poly(A) and globin mRNA. The binding of these substrates is greater than that obtained with other natural or artificial polyribonucleotides. The mRNP fraction also binds poly(A) and Met-tRNA-f. Since the factor which binds initiator tRNA also binds poly(A) and mRNA, and this activity can be found on mRNPs, there may be a relationship between initiator tRNA binding and messenger binding in early events of eukaryotic initiation.
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PMID:Interaction of poly(A) and mRNA with eukaryotic initiator met-tRNA-f binding factor: identification of this activity on reticulocyte ribonucleic acid protein particles. 105 61

A ribonucleoprotein complex isolated from rabbit thymus nuclear lysates was found to be an inhibitor of DNA-dependent RNA polymerase II. The inhibition appeared to be of a competitive type and was completely reversed by high concentration of DNA. Highest inhibition was observed when enzyme and complex were preincubated before addition of DNA while there was little inhibition after enzyme had started synthesis on the DNA template. The RNA isolated from the complex was equally inhibitory and was a more effective inhibitor than either tRNA or rRNA.
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PMID:Nuclear ribonucleoproteins as inhibitors of mammalian RNA polymerase. 125 74

The Mauriceville and Varkud plasmids are retroid elements that propagate in the mitochondria of some Neurospora spp. strains. Previous studies of endogenous reactions in ribonucleoprotein particle preparations suggested that the plasmids use a novel mechanism of reverse transcription that involves synthesis of a full-length minus-strand DNA beginning at the 3' end of the plasmid transcript, which has a 3' tRNA-like structure (M. T. R. Kuiper and A. M. Lambowitz, Cell 55:693-704, 1988). In this study, we developed procedures for releasing the Mauriceville plasmid reverse transcriptase from mitochondrial ribonucleoprotein particles and partially purifying it by heparin-Sepharose chromatography. By using these soluble preparations, we show directly that the Mauriceville plasmid reverse transcriptase synthesizes full-length cDNA copies of in vitro transcripts beginning at the 3' end and has a preference for transcripts having the 3' tRNA-like structure. Further, unlike retroviral reverse transcriptases, the Mauriceville plasmid reverse transcriptase begins cDNA synthesis directly opposite the 3'-terminal nucleotide of the template RNA. The ability to initiate cDNA synthesis directly at the 3' end of template RNAs may also be relevant to the mechanisms of reverse transcription used by LINEs, group II introns, and other non-long terminal repeat retroid elements.
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PMID:The Mauriceville plasmid of Neurospora crassa: characterization of a novel reverse transcriptase that begins cDNA synthesis at the 3' end of template RNA. 138 91

The nucleocapsid protein (NC) of all animal retroviruses, encoded by the gag gene, is the major structural protein of the core ribonucleoprotein complex, bound to genomic RNA in mature virions. NC is also thought to play one or more accessory roles in reverse transcription. Mature NC (p7NC) from human immunodeficiency virus type 1 (HIV-1) is a 71-amino acid, basic protein which contains two Cys3His Zn(II) retroviral-type zinc finger domains. Herein, we describe the subcloning and expression of HIV-1 NC, denoted NC71, from an inducible phage T7 RNA polymerase promoter in Escherichia coli. Purified NC71 can be reversibly reconstituted with 2 g.at Zn(II) determined by atomic absorption. Ultraviolet circulation dichroism spectroscopy has been used to characterize the complexes between highly purified NC71 and the RNA homopolynucleotide poly(A) and E. coli tRNA(mixed). On poly(A), Zn2 NC71 is characterized by an apparent site size n = 15 +/- 3 nucleotides and high affinity (Kapp = 3 x 10(7) M-1) and moderately cooperative (omega approximately 170 +/- 25) binding. A mixture of E. coli tRNA species (tRNA(mixed) was used to probe the conformational changes induced in tRNA upon binding of HIV-1 NC71. Two structural forms of tRNA(mixed), which differ in their degree of tertiary structure, were assayed for their susceptibility to denaturation by NC71. Five molar monomer equivalents of NC71 are required to denature the "inactive" tRNA in the absence of Mg2+. A Zn(II)-free, oxidized form of NC71 was also shown to unwind inactive tRNA with the same efficiency and stoichiometry. The detailed spectral changes which occur on NC-induced denaturation closely mimic temperature-induced denaturation of inactive tRNA(mixed). The prototype helix-destabilizing protein, T4 gene 32 protein, is unable to unwind this form of tRNA under the same conditions. The stoichiometry of unwinding of inactive tRNA by NC71 is consistent with the site size determined with poly(A). An "active" form of tRNA(mixed), prepared by thermal denaturation and refolding of the inactive form with Mg2+, proved less susceptible to both temperature and NC71-induced unwinding. The mechanistic implications of these findings on the reported biochemical activities of RNA:RNA annealing and replication primer tRNA positioning by NC are discussed.
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PMID:Recombinant human immunodeficiency virus type 1 nucleocapsid (NCp7) protein unwinds tRNA. 155 77

Rat liver ribonuclease P was isolated from a cytosolic fraction and shown to have optimal activity in the presence of 1 mM MgCl2 and 150-200 mM KCl using Escherchia coli pre-tRNA(Tyr) as substrate. In cesium sulfate isopycnic density gradients, the enzyme had a buoyant density of 1.36 g/ml, indicating that it is a ribonucleoprotein complex. Analysis of the RNAs in the enzyme sample purified through two successive Cs2SO4 density gradient steps revealed the copurification of two major species of RNA (RRP1 and RRP2) along with several less abundant RNAs. Rat liver ribonuclease P activity was insensitive to micrococcal nuclease pretreatment. However, the nuclease-treated preparations contained several incompletely degraded RNA species that may have been sufficient to support the ribonuclease P activity. When RNase A was substituted for micrococcal nuclease, the ribonuclease P activity was diminished by greater than 90%, suggesting the requirement for an RNA subunit for activity.
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PMID:Characterization of ribonuclease P isolated from rat liver cytosol. 160 34

Ribonuclease P RNA is the catalytic moiety of the ribonucleoprotein enzyme that removes precursor sequences from 5'-ends of pre-tRNAs. A photoaffinity cross-linking agent was coupled to the substrate phosphate on which RNase P acts and used to map nucleotides in the vicinity of the catalytic site of this ribozyme. Mature tRNA(Phe) containing a 5'-thiophosphate was synthesized by transcription in vitro using phage T7 RNA polymerase in the presence of guanosine 5'-phosphorothioate. The photoagent (azidophenacyl) was coupled uniquely to the 5'-thiophosphate of the tRNA, the site of action by RNase P. The photoagent-containing tRNA binds to RNase P RNA and is cross-linked by UV irradiation to it at high efficiency (10-30%). Cross-linked conjugates are enzymatically inactive, consistent with the occupancy of the active site of the RNase P RNA by the tRNA. Reversal of the cross-link by phenylmercuric acetate restores activity. The sites of cross-linking in RNase P RNA were determined by primer extension. In order to identify generalities and detect idiosyncrasies, analyses were carried out using RNase P RNAs from three phylogenetically diverse organisms: Bacillus subtilis, Chromatium vinosum and Escherichia coli. In the context of a phylogenetic structure model, two regions of cross-linking are observed in all three RNAs. Two of the RNAs cross-link to a lesser extent at a third structural region and one of the RNAs is cross-linked to a small extent to a fourth region. All the sites of cross-linking between the substrate phosphate in tRNA and the RNase P RNAs are in the conserved core of the structure model, consistent with the importance of the cross-linked residues to the action of this RNA enzyme.
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PMID:Mapping the active site of ribonuclease P RNA using a substrate containing a photoaffinity agent. 170 Nov 42


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