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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We provide biochemical evidence demonstrating that membrane encapsidated structures present in terminal gastric patients share similar features with retrovirus-like particles. Purified particles reveal few polypeptides, one of them glycosylated. A ribonucleoprotein core-like component is recovered which retains the DNA-polymerizing activity and contains at least one RNA component which can be efficiently translated in vitro.
Cell Mol Biol (Noisy-le-grand) 1992 Dec
PMID:Biochemical evidence associating membrane-encapsidated particles with reverse transcription in human gastric cancer. 128 26

Encapsidation of presynthesized and nascent (synthesized de novo) vesicular stomatitis virus (VSV) leader RNA in vitro by the nucleocapsid protein (N) and the role of the phosphoprotein (P, previously known as NS) in this process were examined. Presynthesized VSV leader RNAs were derived from the SP6 transcription vectors containing both (+) and (-) leader genes while the nascent RNA was derived from transcription of viral ribonucleoprotein (RNP) complex. The N and the P proteins were made by transcription from SP6 vectors containing the genes, followed by translation of the mRNAs in rabbit reticulocyte lysate. Here, we demonstrate that the N protein alone encapsidated presynthesized VSV leader RNA; however, prior formation of N-P complex totally abolished the encapsidation property of N. On the other hand, encapsidation of nascent RNA by the N protein was stimulated by the N-P complex. These results suggest that encapsidation by the N protein of presynthesized and nascent VSV RNA are separate biochemical processes which can be distinguished by the differential role of the phosphoprotein P in the two reactions.
Cell Mol Biol 1992 Feb
PMID:Role of the phosphoprotein (P) in the encapsidation of presynthesized and de novo synthesized vesicular stomatitis virus RNA by the nucleocapsid protein (N) in vitro. 131 45

Epstein-Barr virus/C3d receptor (CR2) is a glycoprotein of mol. wt 140,000 expressed on the surface of Raji cells. We previously isolated phosphorylated CR2 from purified Raji cell nuclei. We have analyzed the nuclear localization of CR2 by electron microscope immunochemistry of thin sections of Raji cells and we have compared the binding properties of CR2 expressed on purified plasma membranes or nuclei. Anti-CR2 mAb immunogold labeling of thin sections of Raji cells identified CR2 at the nuclear surface and also within the nucleus. Nuclear envelope associated CR2 was localized mainly at nuclear pores. Within the nucleus, CR2 was associated with ribonucleoprotein (RNP) interchromatin fibrils. This labeling was preserved in nuclear matrix preparations. CR2 expressed on the surfaces of purified nuclei or on the cell surface interacted with soluble and particle-bound C3bi/C3d. Monoclonal anti-CR2 antibodies, which recognized extracellular domains of CR2, reacted differently with CR2 depending on its subcellular localization. The presence of CR2 in nuclei may be due to translocation of the cell surface CR2 and/or the presence of two distinct intracellular pathways for mature CR2.
Mol Immunol 1992 Sep
PMID:Nuclear localization of the Epstein-Barr virus/C3d receptor (CR2) in the human Burkitt B lymphoma cell, Raji. 132 59

The human Y RNAs, small RNAs with an unknown function, are complexed with at least three proteins: the 60,000 M(r) Ro protein (Ro60), the 52,000 M(r) Ro protein (Ro52) and the La protein (La). In this study we examined the intermolecular interactions between the components of these so-called Ro ribonucleoprotein (Ro RNP) complexes. Incubation of 32P-labelled hY1 RNA in HeLa S100 extract allows the reconstitution of Ro RNP complexes, which were analysed by immunoprecipitation with monospecific antisera. By immunodepletion of HeLa S100 extracts for either Ro60, Ro52 or La, followed by supplementation with recombinant Ro60 or La, it was demonstrated that both Ro60 and La bind to hY1 RNA directly without being influenced by one of the other proteins. However, binding of Ro52 to hY1 RNA required the presence of Ro60, which strongly suggests that the association of Ro52 with Ro RNPs is mediated by protein-protein interactions between Ro60 and Ro52.
J Mol Biol 1992 Sep 20
PMID:Ro ribonucleoprotein assembly in vitro. Identification of RNA-protein and protein-protein interactions. 138 50

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.
Mol Cell Biol 1992 Nov
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

Pre-mRNA processing in eukaryotic cells requires the participation of multiple protein factors and ribonucleoprotein particles. One class of proteins involved in this process are RNA-binding proteins, which contain a domain of ca. 90 amino acids with a characteristic ribonucleoprotein consensus sequence (RNP-CS). A PCR approach that is suitable for the characterization of RNP-CS-type proteins is described. Fifteen different RNA-binding domains were amplified from Nicotiana tabacum (tobacco) using oligonucleotide primers specific for the sequences (K/R)G(F/Y)(G/A)FVX(F/Y) and (L/I/V)(F/Y)(V/I)(G/K)(N/G)L, which are conserved in known RNP-CS proteins. Using the tobacco domains as probes, cDNAs encoding two RNA-binding proteins, each containing two RNP-CS-type domains, were characterized in N. plumbaginifolia. The proteins, designated CP-RBP30 and CP-RBP31, are targeted to chloroplasts as demonstrated by expression of epitope-tagged cDNAs in transfected protoplasts, followed by indirect immunofluorescence. High levels of mRNA for each protein were found in leaves but not in roots, and expression of the CP-RBP31 mRNA was strongly regulated by light. The N. plumbaginifolia proteins described in this work are distinct from chloroplast RNA-binding proteins characterized recently in tobacco and spinach.
Mol Gen Genet 1992 Sep
PMID:Multiple plant RNA binding proteins identified by PCR: expression of cDNAs encoding RNA binding proteins targeted to chloroplasts in Nicotiana plumbaginifolia. 140 85

The Trypanosoma brucei spliced leader (SL) RNA donates its 5' leader sequence to all nuclear pre-mRNAs via trans RNA splicing. The SL RNA is a small-nuclear U RNA-like molecule which is present in the cell as part of a small ribonucleoprotein particle. However, unlike the trimethylguanosine-capped small nuclear U RNAs, the SL RNA has a highly modified 5' terminus containing an m7G cap and methylations on the first four transcribed nucleotides. Here, we show that incubation of procyclic-form T. brucei in the presence of the S-adenosylmethionine analog, sinefungin, leads to a rapid inhibition of SL RNA methylation. A concomitant inhibition of trans splicing and an accumulation of high-molecular-weight tubulin transcripts were also observed. The effects of sinefungin on SL RNA methylation and on trans splicing were correlated by labeling of cells incubated in the presence of the antibiotic. The results indicate that 5' modifications of the SL RNA are necessary for it to participate in trans splicing. SL RNA modification is not required for assembly of the core SL ribonucleoprotein, as these Cs2SO4-resistant particles can be formed with either methylated or undermethylated SL RNA.
Mol Cell Biol 1992 Nov
PMID:Trypanosoma brucei spliced-leader RNA methylations are required for trans splicing in vivo. 140 66

We showed previously that a branch site mutation in simian virus 40 early pre-mRNA that prevented small t antigen mRNA splicing could be efficiently suppressed by a compensatory mutation in a coexpressed U2 small nuclear (sn) RNA gene. We have now generated second-site mutations in this suppressor gene to investigate regions of U2 RNA required for function. A number of mutations in a putative stem at the 5' end of the molecule inhibited splicing, indicating that bases in this region are important for activity. However, several lines of evidence suggested that formation of the entire stem is not essential for splicing. Indeed, mutations that strengthen the stem actually inhibited splicing, and evidence that this prevents a required base-pairing interaction with U6 snRNA is presented. These results suggest that the relative stabilities of competing intra- and intermolecular base-pairing interactions play an important role in the splicing reaction. Mutations in a conserved single-stranded region immediately 3' to the branch site recognition sequence all inhibited splicing, indicating that this region is required for U2 function, although its exact role remains unknown. Finally, two mutations in the loop of stem IV at the 3' end of the molecule, which destroy the binding site of U2 sn ribonucleoprotein B", prevented small t splicing; this finding contrasts with previous studies which utilized different assay systems. Analysis of the accumulation and subcellular localization of all of the mutant RNAs showed that they were similar to those of the parental suppressor U2 RNA, indicating that the effects observed indeed reflect defects in splicing.
Mol Cell Biol 1992 Dec
PMID:Multiple functional domains of human U2 small nuclear RNA: strengthening conserved stem I can block splicing. 144 79

The major coat-protein-binding element of turnip crinkle virus RNA was previously mapped in the region of the UAG termination codon in the viral polymerase gene. This region encompasses two of the high-affinity coat-protein-binding sites (Fa and Ff) that we suggested were physically associated in a stem-loop in a ribonucleoprotein complex involved in assembly initiation (Wei, Heaton, Morris, and Harrison, J. Mol. Biol. 214, 85-95, 1990). We have also demonstrated that this RNA element was capable of specific coat protein binding in vitro (Wei and Morris, J. Mol. Biol. 222, 437-443, 1991). We now provide physical evidence, by in vitro chemical and enzymatic probing of the viral RNA, that support the suggestion that the two coat-protein-binding sites base pair to form a stem structure (A/F stem) surrounding the UAG terminator in wild-type RNA. We have shown here that a mutant with seven conservative nucleotide substitutions in Fa does not accumulate to detectable levels in plants or protoplasts and that the A/F stem structure is drastically altered in this mutant. We suggest that the primary effect of this mutation is on replication rather than on a reduction in RNA stability resulting from a defect in encapsidation of the virion RNA because previous results have shown that encapsidation-deficient mutants have little or no effect on viral RNA replication (Hacker, Petty, Wei, and Morris, Virology 186, 1-8, 1992). The analysis of the A/F stem was extended by construction and characterization of a series of mutants and revertants that displayed variable levels of replication deficiency but minimal concomitant defect in encapsidation efficiency. The extent of the replication defect correlated with the predicted destabilization of the A/F stem structure. We conclude from these results that this RNA element is involved in viral replication, and we tentatively suggest that the A/F stem structure may be functionally involved in the readthrough translation of the viral polymerase.
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PMID:Characterization of an internal element in turnip crinkle virus RNA involved in both coat protein binding and replication. 152 38

We have identified and characterized a U6 small nuclear (sn) ribonucleoprotein particle (RNP) present in the nuclei of Xenopus laevis oocytes. The structure of this U6 snRNP was investigated by native gel shift analysis and a combination of RNA-protein UV cross-linking, RNase T1 fingerprinting, and immunoprecipitation assays. These analyses demonstrate that certain forms of U6 snRNA associate with the 50-kDa nuclear antigen La both in vivo and in vitro. The La protein binds the stretch of uridylates at the 3' hydroxyl end of newly synthesized U6 snRNA. La does not bind to mature U6 snRNAs that have 2',3'-cyclic phosphate (greater than p) groups at their 3' ends (E. Lund and J. E. Dahlberg, Science 255:327-330, 1992) or to U6 snRNAs in anti-Sm-precipitable U4/U6 snRNPs. We propose that 3'-end modification, including posttranscriptional UMP addition, modulates the binding of La protein to U6 snRNA which, in turn, may affect the function of this RNA.
Mol Cell Biol 1992 Jul
PMID:3'-end-dependent formation of U6 small nuclear ribonucleoprotein particles in Xenopus laevis oocyte nuclei. 153 84


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