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:3.1.26.9 (ribonuclease)
6,589 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have described an in vitro system in which active su+III tRNATyr is synthesized from a phi80psu++III DNA template. Using this system, we have identified four essential components that are required for synthesis of tRNA. The first of these is DNA-dependent RNA polymerase. It has been shown that a crude preparation of DNA-dependent RNA polymerase synthesizes su++III tRNATyr precursor similar to that which has been isolated in vivo, and that this preparation is capable of supporting high levels of tRNA synthesis. With purified DNA-dependent RNA polymerase, the su++III tRNATyr precursor was not observed as a transcription product and tRNA synthesis was below detetable levels. On this basis, a second essential component for tRNA synthesis was identified. This fraction, designated Fraction V, in combination with purified RNA polymerase, catalyzes the synthesis of precursor tRNA. The third component is a ribonuclease (RNase P III), which specifically catalyzes the removal of the extra nucleotides present at the 3' terminus of the tRNA precursor. In the absence of this fraction, the in vitro synthesized su++III tRNATyr is slightly larger than 4 S and contains additional nucleotides beyond the normal --CCAOH 3 terminus of the mature tRNA. The fourth essential component required is a fraction containing RNase P, a previously identified endonuclease which specifically catalyzes the removal of the 5' extra nucleotides present on tRNA precursors.
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PMID:In vitro synthesis of transfer RNA. I. Purification of required components. 109 89

We have shown that the synthesis of active su+III tRNATyr from a phi80psu+III DNA template requires the action of four distinct enzymatic activities. The first of these, DNA-dependent RNA polymerase, catalyzes the formation of a large molecular weight transcript, initiating synthesis at a specific site 41 nucleotides proximal to the 5' end of the su+III tRNATyr structural gene and continuing at least 100 nucleotides beyond the 3' terminus of the su+III tRNATyr sequence. The second required component, designated Fraction V, allows purified DNA-DEPENDENT RNA polymerase to function in tRNA synthesis. We have shown that this fraction contains an endonuclease that together with DNA-dependent RNA polymerase is responsible for the synthesis of su+III tRNATyr "precursor". Thus, su+III tRNATyr precursor is not itself the primary transcription product of the su+III tRNATyr gene, but rather, it arises as a result of post-transcriptional cleavage of a much larger transcript by the action of the nuclease present in Fraction V. The third enzymatic activity required for synthesis of active su+III tRNATyr is a ribonuclease (RNase P III) that specifically catalyzes the removal of the 3' extra nucleotides from the su+III tRNATyr precursor. The fourth activity required for synthesis of tRNA is a previously identified endonuclease, RNase P, that specifically catalyzes the removal of the 5' extra nucleotides from tRNA precursors. The properties of RNase P purified according to the procedure developed in this laboratory have been compared with those of the enzyme purified from ribosomes according to the procedure described by Robertson et al. (Robertson, H.D., Altman, S., and Smith, F.D. (1972) J.Biol. Chem. 247, 5243-5251.).
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PMID:In vitro synthesis of transfer RNA. II. Identification of required enzymatic activities. 109 90

tRNAIIArg purified from bulk brewers' yeast tRNA by countercurrent distribution followed by two column-chromatographic steps was completely digested with pancreatic and T1 ribonucleases. Isolations of the products have been carried out either by column chromatography or by high-voltage electrophoresis. Analyses of the isolated nucleotides and olignoucleotides were in good agreement and indicate that this tRNA is composed of 76 nucltotide residues including 13 minor nucleotides. Overlaps resulting from the end-products of the two complementary digests led to a sequence of 25 residues. The primary structure of tRNAIIArg has been determined after partial digestion with T1 ribonuclease as described in the following paper.
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PMID:The primary structure of tRNAIIArg from brewers' yeast. 1. Complete digestions with pancreatic and T1 ribonucleases. 110 Mar 95

The enrichment of tRNA at specific sites with carbon-13 has been accomplished in vivo using a mutant of Escherichia coli. A relaxed strain of E. coli auxotrophic for methionine was grown in a specifically defined medium supplemented with either [14C] or [13C]-methyl labeled methionine. Cells were collected at the end of the log-phase of growth and tRNA was extracted. Analysis of the radioactivity of the [14C]-labeled tRNA established an incorporation ratio of three labeled carbons per tRNA molecule. Incorporation of the [14C]-label in vivo was confined to the methylation of nucleotides as determined by thin layer chromatography of nucleotides resulting from a ribonuclease digestion of [14C]-labeled tRNA. The carbon-13 NMR spectrum of [13C]-enriched tRNA indicated a similar degree of incorporation into the methylated nucleotides by the substantial enhancement of [13C]-methyl NMR signals only. Assignment of signals has been made for the methyl groups of ribothymidine and N7-methylguanosine in E. coli tRNA.
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PMID:Utilization of an Escherichia coli mutant for carbon-13 enrichment of tRNA for NMR studies. 110 Dec 25

Mild ribonuclease treatment of the membrane fraction of P3K cells released three types of membrane-bound ribosomal particles: (a) all the newly made native 40S subunits detected after 2 h of [3H]uridine pulse. Since after a 3-min pulse with [35S]methionine these membrane native subunits appear to contain at least sevenfold more Met-tRNA per particle than the free native subunits, they may all be initiation complexes with mRNA molecules which have just become associated with the membranes; (b) about 50% of the ribosomes present in polyribosomes. Evidence is presented that the released ribosomes carry nascent chains about two and a half to three times shorter than those present on the ribosomes remaining bound to the membranes. It is proposed that in the membrane-bound polyribosomes of P3K cells, only the ribosomes closer to the 3' end of the mRNA molecules are directly bound, while the latest ribosomes to enter the polyribosomal structures are indirectly bound through the mRNA molecules; (c) a small number of 40S subunits of polyribosomal origin, presumably initiation complexes attached at the 5' end of mRNA molecules of polyribosomes. When the P3K cells were incubated with inhibitors acting at different steps of protein synthesis, it was found that puromycin and pactamycin decreased by about 40% the proportion of ribosomes in the membrane fraction, while cycloheximide and anisomycin had no such effect. The ribosomes remaining on the membrane fraction of puromycin-treated cells consisted of a few polyribosomes, and of an accumulation of 80S and 60S particles, which were almost entirely released by high salt treatment of the membranes. The membrane-bound ribosomes found after pactamycin treatment consisted of a few polyribosomes, with a striking accumulation of native 60S subunits and an increased number of native 40S subunits. On the basis of the observations made in this and the preceding papers, a model for the binding of ribosomes to membranes and for the ribosomal cycle on the membranes is proposed. It is suggested that ribosomal subunits exchange between free and membrane-bound polyribosomes through the cytoplasmic pool of free native subunits, and that their entry into membrane-bound ribosomes is mediated by mRNA molecules associated with membranes.
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PMID:Membrane-bound ribosomes of myeloma cells. III. The role of the messenger RNA and the nascent polypeptide chain in the binding of ribosomes to membranes. 117 34

The major RNA species present in the purified mitochondrial fraction of the Walker carcinoma were investigated in order to determine which of them are located in the mitochondria and coded by the organelle DNA. The subcellular distribution of these RNA's and the in vivo sensitivity of the transcription process to selective inhibitors were examined. Among the different species separated by polyacrylamide gel electrophoresis, only the 21 and 16 Se RNA's were found exclusively in the purified mitochondria, approximately Se being the S value estimated from the relative electrophoretic mobility of the RNA. A bifid peak observed in the 16-15 Se region was shown to be an artifact caused by the ribonuclease inhibitor, naphthalene disulfonate. Ethidium bromide at high doses inhibited the incorporation in vivo of 32P into 21, 16, and 4 Se RNA, but the nuclear transcription of cytoplasmic RNA was also inhibited to the same extent. No significant effect was observed at lower doses. In contrast, actinomycin D exerted a differential inhibition of the synthesis of 28 and 18 Se RNA from both the cytoplasmic and the mitochondrial fractions, practically without affecting the transcription of the 21 and 16 Se species. The incorporation of 32P into mitochondrial 4 Se RNA was also considerably more resistant to the drug than the synthesis of the cytoplasmic tRNA. It is concluded that the 21, 16, and Se RNA's are the only major discrete species transcribed from mitochondrial DNA present in the Walker carcinoma.
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PMID:Identification of the products of mitochondrial transcription in the walker corcinosarcoma by the use of actinomycin D and ethidium bromide. 126 33

The formation of a stable complex between glutamyl-tRNA synthetase and the first enzyme of chlorophyll biosynthesis glutamyl-tRNA reductase was investigated in the green alga Chlamydomonas reinhardtii. Apparently homogenous enzymes, purified after previously established purification protocols were incubated in various combinations with ATP, glutamate, tRNA(Glu) and NADPH and formed complexes were isolated via glycerol gradient centrifugation. Stable complexes were detected only after the preincubation of glutamyl-tRNA synthetase, glutamyl-tRNA reductase with either glutamyl-tRNA or free tRNA(Glu), ATP and glutamate, indicating the obligatory requirement of aminoacylated tRNA(Glu) for complex formation. The further addition of NADPH resulting in the reduction of the tRNA-bound glutamate to glutamate 1-semialdehyde led to the dissociation of the complex. Once complexed to the two enzymes tRNA(Glu) was found to be partially protected from ribonuclease digestion. Escherichia coli, Bacillus subtilis and Synechocystis 6803 tRNA(Glu) were efficiently incorporated into the protein-RNA complex. The detected complexes provide the chloroplast with a potential channeling mechanism for Glu-tRNA(Glu) into chlorophyll synthesis in order to compete with the chloroplastic protein synthesis machinery.
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PMID:Complex formation between glutamyl-tRNA synthetase and glutamyl-tRNA reductase during the tRNA-dependent synthesis of 5-aminolevulinic acid in Chlamydomonas reinhardtii. 145 6

The pyrE gene, encoding the pyrimidine biosynthetic enzyme orotate phosphoribosyltransferase, is the promoter distal gene of the dicistronic orfE-pyrE operon. The promoter proximal orfE gene, whose transcription and translation is important for regulation of the pyrE attenuator, encodes a 238-amino acid residue protein which was recently identified as the phosphorolytic ribonuclease, RNase PH, that removes nucleotides from the 3' ends of tRNA precursors. In this paper we report the construction of a plasmid, which overexpresses the orfE and pyrE gene products substantially, as well as the purification of the OrfE protein by ammonium sulfate precipitation and chromatography on phosphocellulose. The highly purified protein catalyzes the phosphorolytic cleavage of poly(A) at a rate of 1.6 mumol/min/mg and the formation of CDP from tRNA-CCA-Cn and orthophosphate at a rate equal to 0.14 mumol/min/mg, as characteristic for RNase PH. OrfE/RNase PH contains helix-turn-helix motifs resembling those in DNA-binding proteins, and it binds nonspecifically to DNA. On SDS gels, OrfE/RNase PH migrates as two distinct protein bands. This heterogeneity might be caused by post-translational modification other than proteolysis, or may be an electrophoretic artifact. The native protein is composed of two or more subunits.
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PMID:Overexpression and rapid purification of the orfE/rph gene product, RNase PH of Escherichia coli. 151 52

The covalent modification of E. coli arginyl-tRNA synthetase by the 2',3'-dialdehyde derivative of tRNA(Arg) (tRNA(oxArg)) resulted in the complete inactivation of the ATP-PPi exchange and aminoacylation activities of the enzyme. Sodium dodecyl sulfate polyacrylamide gel electrophoresis of the ArgRS-tRNA(oxArg) covalent complexes indicated that two bands simultaneously appeared on the gel parallel with inactivation corresponding to different higher molecular weights. This result was different from that of the other aminoacyl-tRNA synthetase labeling systems as previously reported. Upon the ribonuclease treatment of the modified ArgRS, less than 15% of both the initial ATP-PPi exchange and aminocylation activities were recovered. During the whole process of labeling and RNase treatment, the two activities of the enzyme were closely associated.
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PMID:Arginyl-tRNA synthetase from Escherichia coli affinity labeling with 3'-oxidized tRNA(Arg). 170 69

Site-directed mutations were introduced in the connecting loops and one of the two stem regions of the RNA pseudoknot in the tRNA-like structure of turnip yellow mosaic virus RNA. The kinetic parameters of valylation for each mutated RNA were determined in a cell-free extract from wheat germ. Structure mapping was performed on most mutants with enzymic probes, like RNase T1, nuclease S1 and cobra venom ribonuclease. An insertion of four A residues in the four-membered connecting loop L1 that crosses the deep groove of the pseudoknot reduces aminoacylation efficiency. Deletions up to three nucleotides do not affect aminoacylation or RNA pseudoknot formation. Deletion of the entire loop abolishes aminoacylation. Although elimination of the pseudoknot is presumed, this could not be demonstrated. Unlike the mutations in loop L1, all mutations in the three-membered connecting loop L2 that crosses the shallow groove of the RNA pseudoknot decrease the aminoacylation efficiency considerably. Nonetheless, the RNA pseudoknot is still present in most mutated RNAs. These results indicate that a number of mutations can be introduced in both loops without abolishing aminoacylation. Results obtained with the introduction of mismatches and A.U base-pairs in stem S1 of the pseudoknot, containing three G.C base-pairs in wild-type RNA, indicate that the pseudoknot is only marginally stable. Our estimation of the gain of free energy due to the pseudoknot formation is at most 2.0 kcal/mol. The pseudoknot structure can, however, be stabilized upon binding the valyl-tRNA synthetase.
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PMID:Mutational analysis of the pseudoknot in the tRNA-like structure of turnip yellow mosaic virus RNA. Aminoacylation efficiency and RNA pseudoknot stability. 173 Oct 70


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