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:3.1.27.1 (RNase)
16,360 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Galactosyltransferase (EC 2.4.1.22) requires bivalent metal ions for its activity. However, preparations of this enzyme solubilized from Golgi membranes of lactating rat mammary gland were shown to be activated not only by Mn2+, Ca2+ and Mg2+, but also by spermine, spermidine, lysyl-lysine, ethylenediamine and other diaminoalkanes, and by a range of basic proteins and peptides, including clupeine, histone, polylysine, ribonuclease, pancreatic trypsin inhibitor, cytochrome c, melittin, avidin and myelin basic protein. Both N-acetyl-lactosamine synthetase and lactose synthetase activities were enhanced. A basic protein fraction was isolated from bovine milk and shown to activate galactosyltransferase at low concentrations. The polyanions ATP, casein, chondroitin sulphate and heparin reversed the activation of galactosyltransferase by several of the above substances. Galactosyltransferase, assayed as a lactose synthetase, showed a 10-fold greater affinity for glucose when Mn2+ ions were replaced by clupeine or by ribonuclease as cationic activator. Evidence was obtained for the presence of an endogenous cationic activator in solubilized Golgi membrane preparations which evoked a similar low apparent Km,glucose. The findings are discussed in the light of cationic activations of glycosyltransferases generally, of the porous nature of the Golgi membrane, and of the unlikelihood of bivalent metal ions being the physiological activators of galactosyltransferase. It is suggested that the natural cationic activator of lactose synthetase may be a secretory protein acting in a manner analogous to the enzyme's activation by alpha-lactalbumin. A scheme is proposed for the two-stage synthesis of lactose and phosphorylation of casein within the cell, to accommodate the apparent incompatibility of these two processes.
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PMID:Cationic activation of galactosyltransferase from rat mammary Golgi membranes by polyamines and by basic peptides and proteins. 310 66

The outer layer of the bacteriophage phi 6 nucleocapsid (NC) was removed by EDTA and reassociated with the core in the presence of Ca2+ or Mg2+. The core was relatively inaccessible to trypsin digestion, was composed of protein P1, and was in the dodecahedral framework reported previously. (H.T. Steely, Jr., and D. Lang, J. Virol. 51:479-483, 1984; Y. Yang and D. Lang, J. Virol. 51:484-488, 1984). The double-stranded RNA genome became RNase sensitive after EDTA treatment of the nucleocapsid.
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PMID:The dodecahedral framework of the bacteriophage phi 6 nucleocapsid is composed of protein P1. 311 Apr 30

In order to determine the mechanism and enzyme(s) responsible for 3' processing of tRNA precursors, we have developed an in vitro processing system that uses as substrates two SP6 RNA polymerase-generated transcripts of the gene for tRNA(Tyrsu3)+ that contain 49 extra 5'-nucleotides and either 5 or 25 extra 3'-nucleotides. A high speed supernatant fraction from an Escherichia coli strain deficient in five ribonucleases was found to accurately process both tRNA precursors in this system to the size of mature tRNA(Tyr). Final 3' end processing of each precursor occurs in an exonucleolytic manner to generate the correct 3' terminus; however, a prior endonucleolytic cleavage also is observed in processing of the longer precursor. The system requires Mg2+ and works optimally at about 50 mM KCl and pH 8-9. Dialysis of the supernatant fraction leads to loss of processing activity but can be restored to normal by the addition of inorganic phosphate or arsenate. Furthermore, nucleoside diphosphates are a product of the processing reaction. These data indicate that 3' processing in RNase-deficient extracts involves a phosphorolytic reaction. On the other hand, phosphate is not required for processing in RNase+ extracts, although it does aid in processing of the longer precursor. The usefulness of this in vitro system for studies of tRNA processing and the identity of the phosphate-requiring enzyme are discussed.
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PMID:3' processing of tRNA precursors in ribonuclease-deficient Escherichia coli. Development and characterization of an in vitro processing system and evidence for a phosphate requirement. 327 67

An endonuclease specific for cruciform junctions has been purified from yeast cells treated with a DNA-damaging agent. The activity was followed through five chromatographic steps by assaying for the linearization of supercoiled plasmid DNA, which extrudes cruciform structures in vitro. The sites of cleavage on pColIR215 were sequenced, and nicks were located to positions symmetrically opposed across the cruciform junction. The products of cleavage were unit length linear duplexes that contained terminal hairpin loops. In contrast to pColIR215, the cleavage patterns of pXG540 plasmid DNA were found to be complex, and cuts were found up to 40 bases from an (A-T)34 sequence that extrudes into a cruciform. Little or no activity could be detected on single-stranded DNA, linear duplex DNA, or nicked circular duplex DNA. The nuclease was insensitive to RNase but was inactivated by treatment with proteinase K. Mg2+ was required as cofactor and could not be replaced by Mn2+, Ca2+, Co2+, or Cu2+. The native molecular weight of the activity was approximately 200,000 as estimated by gel filtration.
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PMID:Purification and properties of a nuclease from Saccharomyces cerevisiae that cleaves DNA at cruciform junctions. 330 13

A DNA-dependent RNA polymerase has been isolated and characterized from the parasitic flagellated protozoan Leishmania mexicana. The initial stages of purification utilized high-ionic-strength extraction and protamine sulfate treatment. The enzyme was further purified by differential elution by heparin-Sepharose, DEAE-Sephadex, and carboxymethyl-Sephadex chromatography. Analysis of the chromatographically purified RNA polymerase on nondenaturing gels revealed two electrophoretic forms. The enzyme isolated had characteristics of true DNA-dependent RNA polymerase since it required DNA and all four nucleoside triphosphates for synthesis of RNase-sensitive products. Analysis of ammonium sulfate and metal ion optima, as well as relative activities of the enzyme with Mn2+ versus Mg2+, gave results similar to those reported for other RNA polymerase IIIs in eucaryotes. Formycin A triphosphate was found to be a noncompetitive inhibitor of RNA polymerase III, and cordycepin triphosphate was found to be inhibitory, although the exact mode of inhibition was not determined.
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PMID:Isolation and characterization of DNA-dependent RNA polymerase III from Leishmania mexicana and inhibition by purine analogs. 343 22

Various rat mammary tumors were analyzed for the presence of a milk-specific Ca2+-stimulated RNase (Ca2+-RNase). When crude extracts of some differentiated tumors--adenocarcinomas of MT/W9, MT/W9a, R3230AC, DMBA-1, DMBA-8, and DMBA-14 and 3MN squamous cell carcinoma--were assayed for RNase activity under various ionic conditions, it was always highest in the presence of Ca2+/EDTA than under any other ionic condition. The opposite was true in invasive MT/W449a and 13762 adenocarcinomas, poorly differentiated SMT/2A carcinomas, MAMF2/TC fibrosarcoma, and MT/A fibroadenoma. Sephacryl S-200 chromatography separation of tumor extracts confirmed the presence of Ca2+-RNase in those differentiated tumors and absence of the enzyme from other tumors. Expressing the activity as a ratio of Ca2+/EDTA to either Mg2+/EDTA or EDTA alone to more clearly represent the relative level of Ca2+-RNase activity further illustrates the distinct differences between tumor classes. Thus Ca2+-RNase is a sensitive marker for use in the characterization of rat tumors with respect to differentiated mammary functions.
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PMID:Milk-specific RNase as a marker of differentiation of rat mammary tumors. 362 52

With the use of a reconstituted poly(ADP-ribosyl)ating enzyme system and three purified nucleases, micrococcal nuclease (MN), bull seminal RNase (BS RNase) and Ca2+, Mg2+-dependent endonuclease (BS DNase), as model acceptor proteins for ADP-ribose, the effect of ionic strength on the modification reaction was examined in detail. When these three nucleases were extensively poly(ADP-ribosyl)ated in this system at a low ionic strength (5 mM Tris), they were all inhibited by about 80% and the chain length of the polymer covalently bound to the nucleases was 13 to 23 ADP-ribose units. The observed inhibition was markedly prevented by increasing the ionic strength in the reaction mixture with a concomitant decrease in the polymer size bound to the nucleases. The NaCl concentrations required for decreasing the extent of the inhibition to half of the maximum were calculated to be 20, 50, and 100 mM for MN, BS RNase, and BS DNase, respectively. These values are similar to the NaCl concentrations required for decreasing the average chain lengths of the polymer to half, suggesting that the length of polymer is closely correlated to the extent of inhibition of these nucleases. DNA-binding affinities of these nucleases, expressed in terms of the NaCl concentrations required for eluting the enzymes from DNA-cellulose, were 140, 280, and 340 mM for MN, BS RNase, and BS DNase, respectively. Considering that maintainance of a ternary complex of poly(ADP-ribose) synthetase, acceptor and DNA may be essential for the modification reaction, the relatively strong salt effect observed in the modification of MN may be explained by its low DNA-binding affinity.
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PMID:Effect of ionic strength on chain elongation in ADP-ribosylation of various nucleases. 371 Oct 53

The 2-thiocytidine residue at position 32 of tRNA1Arg from Escherichia coli was modified specifically with three photoaffinity reagents of different lengths, and the corresponding N-acetylarginyl-tRNA1Arg derivatives were cross-linked to the P site of E. coli 70S ribosomes by irradiation. Covalent attachment was dependent upon the presence of a polynucleotide template and exposure to light of the appropriate wavelength. From 4% to 6% of the noncovalently bound tRNA became cross-linked to the ribosome as a result of photolysis, and attachment to the P site was confirmed by the reactivity of arginine in the covalent complexes toward puromycin. Analysis of the irradiated ribosomes by sucrose-gradient sedimentation at low Mg2+ concentration revealed that the tRNA was associated exclusively with the 30S subunit in all cases. Two of the N-acetylarginyl-tRNA1Arg derivatives were attached primarily to ribosomal proteins whereas the third was cross-linked mainly to 16S RNA. Partial RNase digestion of the latter complex demonstrated that the tRNA had become attached to the 3' third of the rRNA molecule. In addition, the tRNA-rRNA bond was shown to be susceptible to cleavage by hydroxylamine and mercaptoethanol.
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PMID:Photochemical cross-linking of tRNA1Arg to the 30S ribosomal subunit using aryl azide reagents attached to the anticodon loop. 390 90

A technique for isolating defined fragments of a large RNA has been developed and applied to a ribosomal RNA. A section of the Escherichia coli rrnB cistron corresponding to the S8/S15 protein binding domain of 16S ribosomal RNA was cloned into a single-stranded DNA phage; after hybridization of the phage DNA with 16S RNA and digestion with T1 ribonuclease, the protected RNA was separated from the DNA under denaturing conditions to yield a 345-base RNA fragment with unique ends (bases 525-869 in the 16S sequence). The secondary structure of this fragment was determined by mapping the cleavage sites of enzymes specific for single-stranded or double-helical RNA. The fragment structure is almost identical with that proposed for the corresponding region of intact 16S RNA on the basis of phylogenetic comparisons [Woese, C. R., Gutell, R., Gupta, R., & Noller, H. (1983) Microbiol. Rev. 47, 621-669]. We conclude that this section of RNA constitutes an independently folding domain that may be studied in isolation from the rest of the 16S RNA. The structure mapping experiments have indicated several interesting features in the RNA structure. (i) The largest bulge loop in the molecule (20 bases) contains specific tertiary structure. (ii) A region of long-range secondary structure, pairing bases about 200 residues apart in the sequence, can hydrogen bond in two different mutually exclusive schemes. Both appear to exist simultaneously in the RNA fragment under our conditions. (iii) The long-range secondary structure and one adjacent helix melt between 37 and 60 degrees C in the absence of Mg2+, while the rest of the structure is quite stable.
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PMID:Secondary structure of a 345-base RNA fragment covering the S8/S15 protein binding domain of Escherichia coli 16S ribosomal RNA. 390 98

Protein synthesis, normally a light-dependent process in isolated mature chloroplasts of Euglena gracilis var. bacillaris will take place in darkness if ATP and Mg2+ (ATP/Mg) are supplied. Either 5 or 10 mM ATP plus 15 mM MgCl2 are optimal and rates equal to those in the light can be obtained. Since ATP and Mg2+ are not stoichiometrically related, and since the optimal Mg2+ concentration is similar to that which stabilizes chloroplast ribosomes in vitro, it is suggested that the chloroplast is freely permeable to Mg2+ under these conditions. Protein synthesis under these conditions is not inhibited appreciably by DCMU, FCCP, cycloheximide, or by the addition of ribonuclease, but is highly sensitive to chloramphenicol. Carbon dioxide fixation is also a light-dependent process in isolated mature chloroplasts from Euglena, but addition of ATP (5 mM) and fructose bisphosphate (5 mM) plus aldolase (1.0 unit/ml) (fructose-1,6-bisphosphate/aldolase) yields CO2 fixation rates in darkness that are 43% of those normally obtained in the light. Mg2+ higher than 1.0 mM (e.g., 16 mM) is somewhat inhibitory. Chlorophyll synthesis from 5-aminolevulinate in 36 h developing chloroplasts from Euglena is also light-dependent, but addition of ATP/Mg and fructose-1,6-bis-phosphate/aldolase in darkness brings about the accumulation of a compound having the same RF on chromatography as protochlorophyllide from Barley; a subsequent brief illumination of the chloroplasts converts this compound to a compound with the RF of chlorophyll. Thus Euglena chloroplasts supplied with appropriate additions can carry out protein synthesis, carbon dioxide fixation and most of chlorophyll synthesis in darkness. This versatility is appropriate in photosynthetic organelles isolated from photo-organotrophic cells.
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PMID:Synthetic abilities of Euglena chloroplasts in darkness. 392 91


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