Search results for "RNA-Dependent RNA Polymerase"
showing 10 items of 40 documents
Changes in protein domains outside the catalytic site of the bacteriophage Qβ replicase reduce the mutagenic effect of 5-azacytidine.
2014
ABSTRACT The high genetic heterogeneity and great adaptability of RNA viruses are ultimately caused by the low replication fidelity of their polymerases. However, single amino acid substitutions that modify replication fidelity can evolve in response to mutagenic treatments with nucleoside analogues. Here, we investigated how two independent mutants of the bacteriophage Qβ replicase (Thr210Ala and Tyr410His) reduce sensitivity to the nucleoside analogue 5-azacytidine (AZC). Despite being located outside the catalytic site, both mutants reduced the mutation frequency in the presence of the drug. However, they did not modify the type of AZC-induced substitutions, which was mediated mainly by …
Evidence for involvement of a nuclear envelope-associated RNA helicase activity in nucleocytoplasmic RNA transport
1990
It seems well established that translocation of at least some mRNAs through the nuclear pore is (1) an energy-dependent process, and (2) dependent on the presence of the poly(A) segment attached to most mRNA species. We describe that RNA helicase (RNA duplex unwindase) activity is present in a nuclear envelope (NE) preparation, which also appears to be involved in nucleocytoplasmic RNA transport. This activity unwinds RNA: RNA hybrids. The helicase has a pH optimum of 7.5 and a temperature optimum of 30 degrees C. Applying the sealed NE vesicle system, it was shown that duplex RNA species are readily released from the vesicles in an unidirectional manner, in contrast to single-stranded RNA,…
Genetic Analysis of Sequences in the 3′ Nontranslated Region of Hepatitis C Virus That Are Important for RNA Replication
2002
ABSTRACT The genome of the hepatitis C virus (HCV) is a plus-strand RNA molecule that carries a single long open reading frame. It is flanked at either end by highly conserved nontranslated regions (NTRs) that mediate crucial steps in the viral life cycle. The 3′ NTR of HCV has a tripartite structure composed of an about 40-nucleotide variable region, a poly(U/UC) tract that has a heterogeneous length, and a highly conserved 98-nucleotide 3′-terminal sequence designated the X tail or 3′X. Conflicting data as to the role the sequences in the 3′ NTR play in RNA replication have been reported. By using the HCV replicon system, which is based on the self-replication of subgenomic HCV RNAs in hu…
Interaction of 68–kDa TAR RNA-binding protein and other cellular proteins with rpion protein-RNA stem-loop
1995
The RNA stem-loop structure of the trans-activating region TAR sequence of human immunodeficiency virus-1 mRNA is the binding site for a number of host cell proteins. A virtually identical set of proteins from HeLa nuclear extracts was found to bind to the predicted RNA hairpin element of prion protein (PrP) mRNA, as demonstrated in UV cross-linking/RNase protection and Northwestern assays. We show that the cellular TAR loop-binding protein, p68, is among those proteins which associate with PrP RNA. Competition experiments with various TAR RNA mutants revealed that binding of partially purified p68 to PrP RNA stem-loop occurs sequence-specifically. The 100-kDa 2-5A synthetase which is invol…
Arabinose nucleoside triphosphates are no inhibitors for DNA-dependent RNA polymerases.
1976
1-Beta-D-arabinofuranosylcytosine-5' -triphosphate and 9-beta-D-arabinofuranosyladenosine-5' -triphosphate were found to have no inhibitory potency for both mammalian DNA-dependent RNA polymerase II and E. coli DNA-dependent RNA polymerase.
The distribution of active RNA polymerase II along the transcribed region is gene-specific and controlled by elongation factors.
2010
In order to study the intragenic profiles of active transcription, we determined the relative levels of active RNA polymerase II present at the 3'- and 5'-ends of 261 yeast genes by run-on. The results obtained indicate that the 3'/5' run-on ratio varies among the genes studied by over 12 log(2) units. This ratio seems to be an intrinsic characteristic of each transcriptional unit and does not significantly correlate with gene length, G + C content or level of expression. The correlation between the 3'/5' RNA polymerase II ratios measured by run-on and those obtained by chromatin immunoprecipitation is poor, although the genes encoding ribosomal proteins present exceptionally low ratios in …
Detection of the norovirus variants GGII.4 hunter and GGIIb/hilversum in Italian children with gastroenteritis.
2006
Noroviruses (NoVs) are important enteric pathogens of humans. Although they exhibit an impressive genetic diversity, few NoV strains appear to predominate worldwide. Limited epidemiological data are available on NoV gastroenteritis in Italy. In this study, we assessed the prevalence of human NoV in Italian children with gastroenteritis by using a reverse-transcription nested polymerase chain reaction (RT-PCR) assay specific for the RNA-dependent RNA polymerase (RdRp) on faecal samples collected throughout the 2004 surveillance activity in Palermo, Italy. NoVs were detected in 47% of the stool samples obtained from children <5 years age, admitted to hospital with acute non-bacterial gastroen…
The crystal structure of bacteriophage Qβ at 3.5 å resolution
1996
Abstract Background: The capsid protein subunits of small RNA bacteriophages form a T=3 particle upon assembly and RNA encapsidation. Dimers of the capsid protein repress translation of the replicase gene product by binding to the ribosome binding site and this interaction is believed to initiate RNA encapsidation. We have determined the crystal structure of phage Qβ with the aim of clarifying which factors are the most important for particle assembly and RNA interaction in the small phages. Results The crystal structure of bacteriophage Qβ determined at 3.5 a resolution shows that the capsid is stabilized by disulfide bonds on each side of the flexible loops that are situated around the fi…
Transcription in bacteriophage f1-infected Escherichia coli: Very large RNA species are synthesized on the phage DNA
1983
Fractionation of pulse-labeled RNA extracted from E. coli cells infected with phage f1 and hybridization of this RNA to f1 DNA reveals that very large species are synthesized on the phage genome. Hybridization of the RNA to specific fragments of f1 DNA shows that, in the infected cell, at least one mRNA is present into which the sequences of genes III, VI, and I are all transcribed together. This result fully explains the polar effect shown by gene III mutants on the expression of genes VI and I (Pratt et al. 1966).
A Trans-amplifying RNA Vaccine Strategy for Induction of Potent Protective Immunity
2019
Here, we present a potent RNA vaccine approach based on a novel bipartite vector system using trans-amplifying RNA (taRNA). The vector cassette encoding the vaccine antigen originates from an alphaviral self-amplifying RNA (saRNA), from which the replicase was deleted to form a transreplicon. Replicase activity is provided in trans by a second molecule, either by a standard saRNA or an optimized non-replicating mRNA (nrRNA). The latter delivered 10- to 100-fold higher transreplicon expression than the former. Moreover, expression driven by the nrRNA-encoded replicase in the taRNA system was as efficient as in a conventional monopartite saRNA system. We show that the superiority of nrRNA- ov…