Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.1.27.5 (RNase)
17,967 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The Escherichia coli rnt gene, which encodes the RNA-processing enzyme RNase T, is cotranscribed with a downstream gene. Complete sequencing of this gene indicates that its coding region encompasses 1,538 amino acids, making it the longest known protein in E. coli. The gene (tentatively termed lhr for long helicase related) contains the seven conserved motifs of the DNA and RNA helicase superfamily II. An approximately 170-kDa protein is observed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of 35S-labeled extracts prepared from cells in which lhr is under the control of an induced T7 promoter. This protein is absent when lhr is interrupted or when no plasmid is present. Downstream of lhr is the C-terminal region of a convergent gene with homology to glutaredoxin. Interruptions of chromosomal lhr at two different positions within the gene do not affect the growth of E. coli at various temperatures in rich or minimal medium, indicating that lhr is not essential for usual laboratory growth. lhr interruption also has no effect on anaerobic growth. In addition, cells lacking Lhr recover normally from starvation, plate phage normally, and display normal sensitivities to UV irradiation and H2O2. Southern analysis showed that no other gene closely related to lhr is present on the E. coli chromosome. These data expand the known size range of E. coli proteins and suggest that very large helicases are present in this organism.
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PMID:The gene for the longest known Escherichia coli protein is a member of helicase superfamily II. 755 21

Escherichia coli rnhA mutants devoid of RNase HI exhibit constitutive stable DNA replication, cSDR, which is thought to be initiated from R-loops stabilized in the absence of RNase HI. We found that a combination of an rnhA and a recG mutation is lethal to the cell. recG mutations that inactivate the helicase activity of RecG protein and inhibit reverse branch migration of Holliday junctions impart phenotypes resembling those of rnhA mutants. Thus, recG mutants display cSDR activity, and recG polA double mutants are inviable as are rnhA polA double mutants. These results suggest that the RecG helicase has a role in preventing R-loop formation. A model that R-loops are formed by assimilation of RNA transcripts into the duplex DNA is discussed. The model further postulates that RecA protein catalyzes this assimilation reaction and that RecG protein counteracts RecA in this reaction, resolves R-loops by its helicase activity, or does both.
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PMID:Escherichia coli RecG and RecA proteins in R-loop formation. 777 96

Constitutive stable DNA replication (cSDR), which uniquely occurs in Escherichia coli rnhA mutants deficient in ribonuclease HI activity, requires RecA function. The recA428 mutation, which inactivates the recombinase activity but imparts a constitutive coprotease activity, blocks cSDR in rnhA mutants. The result indicates that the recombinase activity of RecA, which promotes homologous pairing and strand exchange, is essential for cSDR. Despite the requirement for RecA recombinase activity, mutations in recB, recD, recJ, ruvA and ruvC neither inhibit nor stimulate cSDR. It was proposed that the property of RecA essential for homologous pairing and strand exchange is uniquely required for initiation of cSDR in rnhA mutants without involving the homologous recombination process. The possibility that RecA protein is necessary to counteract the action of Tus protein, a contra-helicase which stalls replication forks in the ter region of the chromosome, was ruled out because introduction of the tus::kan mutation, which inactivates Tus protein, did not alleviate the RecA requirement for cSDR.
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PMID:RecA, Tus protein and constitutive stable DNA replication in Escherichia coli rnhA mutants. 807 83

The RecG protein of Escherichia coli is a DNA helicase that promotes branch migration of the Holliday junctions. We found that overproduction of RecG protein drastically decreased copy numbers of ColE1-type plasmids, which require R-loop formation between the template DNA and a primer RNA transcript (RNA II) for the initiation of replication. RecG efficiently inhibited in vitro ColE1 DNA synthesis in a reconstituted system containing RNA polymerase, RNase HI and DNA polymerase I. RecG promoted dissociation of RNA II from the R-loop in a manner that required ATP hydrolysis. These results suggest that overproduced RecG inhibits the initiation of replication by prematurely resolving the R-loops formed at the replication origin region of these plasmids with its unique helicase activity. The possibility that RecG regulates the initiation of a unique mode of DNA replication, oriC-independent constitutive stable DNA replication, by its activity in resolving R-loops is discussed.
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PMID:ATP-dependent resolution of R-loops at the ColE1 replication origin by Escherichia coli RecG protein, a Holliday junction-specific helicase. 900 81

Chromosome replication in Escherichia coli is normally initiated at oriC, the origin of chromosome replication. E. coli cells possess at least three additional initiation systems for chromosome replication that are normally repressed but can be activated under certain specific conditions. These are termed the stable DNA replication systems. Inducible stable DNA replication (iSDR), which is activated by SOS induction, is proposed to be initiated from a D-loop, an early intermediate in homologous recombination. Thus, iSDR is a form of recombination-dependent DNA replication (RDR). Analysis of iSDR and RDR has led to the proposal that homologous recombination and double-strand break repair involve extensive semiconservative DNA replication. RDR is proposed to play crucial roles in homologous recombination, double-strand break repair, restoration of collapsed replication forks, and adaptive mutation. Constitutive stable DNA replication (cSDR) is activated in mhA mutants deficient in RNase HI or in recG mutants deficient in RecG helicase. cSDR is proposed to be initiated from an R-loop that can be formed by the invasion of duplex DNA by an RNA transcript, which most probably is catalyzed by RecA protein. The third form of SDR is nSDR, which can be transiently activated in wild-type cells when rapidly growing cells enter the stationary phase. This article describes the characteristics of these alternative DNA replication forms and reviews evidence that has led to the formulation of the proposed models for SDR initiation mechanisms. The possible interplay between DNA replication, homologous recombination, DNA repair, and transcription is explored.
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PMID:Stable DNA replication: interplay between DNA replication, homologous recombination, and transcription. 918 11

A single base change in the helicase superfamily 1 domain of the yeast Saccharomyces cerevisiae SEN1 gene results in a heat-sensitive mutation that alters the cellular abundance of many RNA species. We compared the relative amounts of RNAs between cells that are wild-type and mutant after temperature-shift. In the mutant several RNAs were found to either decrease or increase in abundance. The affected RNAs include tRNAs, rRNAs and small nuclear and nucleolar RNAs. Many of the affected RNAs have been positively identified and include end-matured precursor tRNAs and the small nuclear and nucleolar RNAs U5 and snR40 and snR45. Several small nucleolar RNAs co-immunoprecipitate with Sen1 but differentially associate with the wild-type and mutant protein. Its inactivation also impairs precursor rRNA maturation, resulting in increased accumulation of 35S and 6S precursor rRNAs and reduced levels of 20S, 23S and 27S rRNA processing intermediates. Thus, Sen1 is required for the biosynthesis of various functionally distinct classes of nuclear RNAs. We propose that Sen1 is an RNA helicase acting on a wide range of RNA classes. Its effects on the targeted RNAs in turn enable ribonuclease activity.
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PMID:The yeast SEN1 gene is required for the processing of diverse RNA classes. 936 56

Prior sequence analysis studies have suggested that bacterial ribonuclease (RNase) Ds comprise a complete domain that is found also in Homo sapiens polymyositis-scleroderma overlap syndrome 100 kDa autoantigen and Werner syndrome protein. This RNase D 3'-->5' exoribonuclease domain was predicted to have a structure and mechanism of action similar to the 3'-->5' exodeoxyibonuclease (proofreading) domain of DNA polymerases. Here, hidden Markov model (HMM) and phylogenetic studies have been used to identify and characterise other sequences that may possess this exonuclease domain. Results indicate that it is also present in the RNase T family; Borrelia burgdorferi P93 protein, an immunodominant antigen in Lyme disease; bacteriophage T4 dexA and Escherichia coli exonuclease I, processive 3'-->5' exodeoxyribonucleases that degrade single-stranded DNA; Bacillus subtilis dinG, a probable helicase involved in DNA repair and possibly replication, and peptide synthase 1; Saccharomyces cerevisiae Pab1p-dependent poly(A) nuclease PAN2 subunit, required for shortening mRNA poly(A) tails; Caenorhabditis elegans and Mus musculus CAF1, transcription factor CCR4-associated factor 1; Xenopus laevis XPMC2, prevention of mitotic catastrophe in fission yeast; Drosophila melanogaster egalitarian, oocyte specification and axis determination, and exuperantia, establishment of oocyte polarity; H.sapiens HEM45, expressed in tumour cell lines and uterus and regulated by oestrogen; and 31 open reading frames including one in Methanococcus jannaschii . Examination of a multiple sequence alignment and two three-dimensional structures of proofreading domains has allowed definition of the core sequence, structural and functional elements of this exonuclease domain.
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PMID:The proofreading domain of Escherichia coli DNA polymerase I and other DNA and/or RNA exonuclease domains. 939 23

Werner's syndrome (WS) is an inherited disease with clinical symptoms which resemble premature aging. The Werner's syndrome gene (WRN), which is located on human chromosome 8p12, encodes a predicted protein of 1432 amino acids and shows significant similarity to DNA helicases. We have cloned the full-length mouse cDNA homologue of the human WRN gene encoding a predicted protein of 1320 amino acids and have obtained a full-length 70 kb genomic clone containing the moWRN gene. This gene has been mapped to chromosome 8A3 in mice. The expression of the moWRN gene was increased during apoptosis after IL-2 deprivation, and decreased in the spleen of aged mice. Lymphoid cells isolated from a patient with WS exhibited increased apoptosis after incubation with anti-Fas but not after incubation with the topoisomerase inhibitor VP16. RNase protection reviled dysregulation of the ICE family of apoptosis molecules in the WS cell line. These results indicate that the WS helicase is involved in certain pathways of apoptosis, and defective WS gene expression leads to accumulation of cells that are highly susceptibility to Fas-induced apoptosis.
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PMID:Effect of age and apoptosis on the mouse homologue of the huWRN gene. 968 77

The human helicase gene SKI2W is located between RD and RP1 in the class III region of the major histocompatibility complex. Transcripts of SKI2W are detectable in RNA samples isolated from multiple tissues. The protein product Ski2w shares striking amino acid sequence similarities to the yeast antiviral protein Ski2p that controls the translation of mRNAs, probably based on the mRNA structural integrity. Whether this translational regulation mechanism for cellular and viral RNAs exists in mammals is under investigation. Antisera against human Ski2w were generated using fusion proteins produced in bacteria or insect cells. Western blot analysis showed that the endogenous Ski2w protein is approximately 140 kDa in size and is enriched in polysomal fractions of cytoplasmic extracts from HeLa cells. Ribosomal profile studies revealed that Ski2w distributed throughout the entire sucrose gradient in the presence of Mg2+, but co-sedimented with the 18S rRNA-containing 40S subunit and the small ribosomal subunit protein S27a in the presence of EDTA. The co-sedimentation of Ski2w with the 40S subunit is not affected by RNase A treatment of the cell extract, or the addition of KCl to 0.5 M, suggesting that Ski2w is associated with the 40S ribosomal subunit. Indirect immunofluorescence experiments showed that human Ski2w is localized in the nucleoli and in the cytoplasm. In essence, human Ski2w is present at the sites of ribosome biogenesis and protein synthesis.
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PMID:The human DEVH-box protein Ski2w from the HLA is localized in nucleoli and ribosomes. 970 21

We report the identification, cDNA cloning, and molecular characterization of a novel, constitutive nucleolar protein. The cDNA-deduced amino acid sequence of the human protein defines a polypeptide of a calculated mass of 61.5 kDa and an isoelectric point of 9.9. Inspection of the primary sequence disclosed that the protein is a member of the family of "DEAD-box" proteins, representing a subgroup of putative ATP-dependent RNA helicases. ATPase activity of the recombinant protein is evident and stimulated by a variety of polynucleotides tested. Immunolocalization studies revealed that protein NOH61 (nucleolar helicase of 61 kDa) is highly conserved during evolution and shows a strong accumulation in nucleoli. Biochemical experiments have shown that protein NOH61 synthesized in vitro sediments with approximately 11.5 S, i.e., apparently as homo-oligomeric structures. By contrast, sucrose gradient centrifugation analysis of cellular extracts obtained with buffers of elevated ionic strength (600 mM NaCl) revealed that the solubilized native protein sediments with approximately 4 S, suggestive of the monomeric form. Interestingly, protein NOH61 has also been identified as a specific constituent of free nucleoplasmic 65S preribosomal particles but is absent from cytoplasmic ribosomes. Treatment of cultured cells with 1) the transcription inhibitor actinomycin D and 2) RNase A results in a complete dissociation of NOH61 from nucleolar structures. The specific intracellular localization and its striking sequence homology to other known RNA helicases lead to the hypothesis that protein NOH61 might be involved in ribosome synthesis, most likely during the assembly process of the large (60S) ribosomal subunit.
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PMID:A novel helicase-type protein in the nucleolus: protein NOH61. 1074 21


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