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)

Because it has been proposed that the ribosome-membrane interaction is different in endoplasmic reticulum derived from a non-secretory and secretory cell we undertook a study to determine whether attachment of the ribosome to the membrane involved ribosomal RNA and if the rRNA in ribosomes derived from the two classes of cell possessed an altered susceptibility to RNAase (ribonuclease) hydrolysis. We found that brain ribosomes appeared to possess more regions accessible to nuclease attack, independent of whether a sequence-dependent RNAase (T(1)) or a sterically hindered RNAase bound to Enzite polymer was employed. These results were independent of whether the ribosomes were membrane-bound or detached from the endoplasmic reticulum membranes, but at high RNAase concentration these differences became negligible. No conclusions, however, could be drawn as to whether ribosomal RNA is involved in the attachment of the ribosome to the endoplasmic reticulum membrane, because of the presence of endogeneous membrane-associated RNAases. Analysis of the rRNA fragments by polyacrylamide-gel electrophoresis suggests that the sites available for attack by low concentrations of nuclease in bound-ribosomes derived from brain cortex are different from those of liver.
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PMID:A comparative study of ribonuclease hydrolysis of rat brain-cortex and liver membrane-bound ribosomes. 476 63

Addition of nutrients to starved mouse S-180 cells leads to rapid conversion of ribosomal monomers to polysomes. During this process, a portion of the ribosomes originally found in the 17,000 g (10 min centrifugation) supernatant of cell lysates becomes firmly attached to structures sedimenting at 500 g (5 min centrifugation). Electron microscopy of sections of the intact cells showed the change from randomly distributed ribosomal particles to clusters. Association with membranes also became evident. The material sedimenting at 500 g comprised nuclei enclosed in an extensive endoplasmic reticulum (ER) network. This fraction prepared from recovering cells showed numerous ribosome clusters associated with the ER network. The appearance of many of these clusters indicated that the ribosomal particles were not directly bound to the membranes. RNase treatment released about 40% of the attached ribosomes as monomers, and ethylenediaminetetraacetic acid released 60% as subunits. It is suggested that during polysome formation a portion of the ribosomes becomes attached to the membranes through the intermediary of messenger RNA.
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PMID:Attachment of ribosomes to membranes during polysome formation in mouse sarcoma 180 cells. 499 71

1. A centrifugation method for the fractionation of the postmitochondrial fraction from rat-liver homogenates is described. The technique, in which no detergent is used, may be used as a tool to discriminate between two classes of ribosomes. One class is firmly bound to membranes and the other consists either of free polysomes or of ribosomes attached by weaker forces to the membranes of the endoplasmic reticulum. 2. Electron-micrograph studies revealed that the polysomes were not contaminated with bound ribosomes or with membranous fragments. 3. The separated fractions were characterized by their RNA, protein, ribonuclease and phospholipid content. 4. The influence of starvation on the RNA and protein contents of the different fractions was investigated. 5. Labelling of the various centrifugal fractions in vivo revealed no difference in uptake of radioactive amino acid between the two classes of ribosomes. 6. Incorporation of radioactive leucine in vitro and the polyuridylic acid-directed phenylalanine incorporation were similar for both classes of ribosomes.
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PMID:Isolation and properties of polyribosomes and fragments of the endoplasmic reticulum from rat liver. 603 56

A cytochemical technique for the ultrastructural localization of substrates using enzyme-gold complexes is reported. RNase A and DNase I have been labeled with gold particles. The RNase-gold and dNase-gold complexes obtained were applied on thin sections of glutaraldehyde-fixed and Epon-embedded tissues. Different cellular compartments were labeled by these enzyme-gold complexes. Using the RNase-gold complex the rough endoplasmic reticulum appeared decorated with gold particles. The gold marker was also present over the nucleus, especially over the nucleolus; mitochondria were weakly labeled. Using the DNase-gold complex, gold particles were concentrated over the euchromatin of the nucleus and the mitochondria. The heterochromatin and the nucleolus showed a less intense labeling. For both enzyme-gold complexes, the Golgi area, the secretory granules and the extracellular space appeared free of label. In those control conditions where the substrates were added to the enzyme-gold complexes a major reduction in the labeling was observed. A quantitative evaluation of the labeling was performed. This evaluation confirmed the qualitative observations and the marked reduction of labeling occurring under the control conditions. The combination of the specificity of the enzyme-substrate interactions with the size and electron density of the gold particles and the good ultrastructural preservation of the tissues resulted in a very specific labeling with high resolution. These results demonstrate the possibility of detecting substrates by means of enzyme-gold complexes at the electron microscope level.
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PMID:Ultrastructural localization of nuclei acids by the use of enzyme-gold complexes. 626 46

An endonuclease, which was originally identified for its RNA polymerase inhibitory activity, was isolated from rat liver endoplasmic reticulum. The enzyme yields on gel chromatography four active fractions of different molecular weights (Mr 5.3 X 10(4), 9 X 10(4), 1.55 X 10(5) and Sephacryl S-200 fraction at V0). Each fraction contains polypeptide chains which give a single band on sodium dodecylsulphate electrophoresis (Mr 5.4 X 10(4). This indicates that the enzyme is an oligomeric protein and each of its subunits exhibits the same or very similar molecular weights. Deoxyribonucleoside and ribonucleoside triphosphates can bind to the endoplasmic reticulum nuclease. Binding is enhanced in the presence of divalent cations particularly Mg2+. The enzyme exhibits mainly RNase activity but can also degrade denatured DNA and DNA . RNA hybrids which contain breaks in one of the two strands. Poly(A) and mainly poly(U) are most susceptible to its nucleolytic activity whereas poly(C) is completely resistant.
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PMID:Endoplasmic reticulum nuclease. Purification and specificity. 627 70

Mammary gland polysomes are difficult to isolate from the lactating rat using methods developed for other species and tissues, most likely due to high calcium-stimulated ribonuclease activity in that tissue. A new method, utilizing ethyleneglycol-bis-(beta-aminoethylether)-N,N'-tetraacetic acid (EGTA) to bind calcium, yields highly aggregated polysomes from lactating rat mammary gland. Fresh mammary tissue is pulverized under liquid nitrogen. Free and membrane-bound polysomes are isolated by differential centrifugation in solutions containing 100 mM KCl, 100 mM MgCl2, 75 mM EGTA, 500 micrograms/ml heparin and 50 mM Tris buffer, pH 8.2 at 5 degrees C. Bound polysomes are released from the endoplasmic reticulum using Triton X-100 and deoxycholate. Polysome profiles are obtained on linear sucrose gradients and scanned at 254 nm. The method gives quantitative recovery of homogenate total RNA. To demonstrate that the method can be used to study nutritional effects on mammary gland polysome aggregation, lactating rats were fasted 22-66 h and then refed a stock diet for 71-95 h. Refeeding increased the percentage of polysomes (trimers or larger) in the bound fraction from 84 +/- 1 to 93 +/- 1% (P less than 0.001) and in the free fraction from 42 +/- 2 to 55 +/- 3% (P less than 0.001).
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PMID:A method for isolation of undegraded free and membrane-bound ribosomes from rat lactating mammary gland. 642 19

Zein synthesis in the developing (22 and 50 days postpollination) endosperm and embryo of maize (Zea mays L.) double mutants, brittle-1; opaque-2 and brittle-2;opaque-2, were compared and correlated with sucrose concentration and RNase activity in order to test the hypothesis that high sucrose concentrations may prevent the interaction between zein polyribosomes and endoplasmic reticulum and make the zein mRNAs more susceptible to hydrolysis by high RNase activity, resulting in a severe reduction in zein synthesis. The double-mutant combinations of opaque-2 with each of the starch-deficient mutants, brittle-1 and brittle-2, maintained not only a high sucrose concentration in the endosperm but also a higher RNase activity than either one of the single mutants alone. Consequently, these double mutants severely suppressed the synthesis of two major zein components in their endosperms. In contrast to the endosperm system, embryos of the double mutants produced amounts of zein (and electrophoretic patterns) similar to that of the opaque-2 embryo, and their embryos contained levels of sucrose and RNase activity comparable to that of the o2 and normal control. These results are consistent with the notion that a posttranscriptional degradation of zein mRNAs by RNase, rather than a specific transcriptional block, is involved in the endosperm to suppress zein synthesis in these double mutants.
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PMID:Zein synthesis in the embryo and endosperm of maize mutants. 649 34

Twenty-two-day-old fetal and five-day-old newborn rats were pretreated with phenobarbital and its hydroxylated metabolites. Drug-metabolizing enzymes (cytochrome P450, epoxide hydrolase, UDP-glucuronosyltransferase, and glutathione-S-transferase) and microsomal ribonuclease were not modified in fetuses treated with 80 or 400 mg . kg-1 of p-hydroxyphenobarbital, in spite of its accumulation in fetal liver. At fetal age, phenobarbital was a poor inducer of drug-metabolizing enzymes. In five-day-old newborns, p-hydroxyphenobarbital provoked a proliferation of endoplasmic reticulum without enzyme induction, whereas phenobarbital induced some drug-metabolizing enzymes. Thus, the effects of p-hydroxyphenobarbital and phenobarbital are retained in five-day-old rats, but undetectable in the fetuses.
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PMID:Comparison of the effects of phenobarbital and its hydroxylated metabolites on drug-metabolizing enzymes during ontogenesis. 681 Feb 95

Ultrastructural studies of Nicotiana clevelandii plants systemically infected with Cymbidium ringspot virus, a member of the tombusvirus group, have shown that a clear-cut relationship exists between perioxisomes and multivesicular bodies (MVB). In infected cells, peroxisomes undergo a progressive vesiculation of the bounding membrane through the possible addition of membranous material by the endoplasmic reticulum and become very plastic. Portions of the ground cytoplasm are engulfed either through the invagination of the limiting membrane or the production of membranous appendages that fold back on the main body. Cytochemical tests have shown MVB to possess catalase and glycolate oxidase activity in the matrix. The vesicles contain RNA, a substantial amount of which is double stranded, as indicated by differential RNase digestion tests in high- and low-salt media. The double-stranded RNA may consist of replicative forms or replicative intermediates of the viral nucleic acid. If so, MVB (i.e., modified peroxisomes) may be directly involved in the replication of Cymbidium ringspot virus.
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PMID:The fine structure of Cymbidium ringspot virus infections in host tissues. III. Role of peroxisomes in the genesis of multivesicular bodies. 684 73

Sera from a patient with systemic lupus erythematosus (SLE), tested by indirect immunofluorescence on frozen tissue sections, gave granular cytoplasmic staining of hepatocytes, gastric chief cells, exocrine cells of the pancreas and submandibular glands, and cerebellar Purkinje cells. In acetone-fixed monolayers of rat embryonic fibroblasts, 3T3 cells, mouse neuroblastoma cells, and cells from a human melanoma and colon carcinoma cell line, the sera stained perinuclear cytoplasmic granules which radiated out towards the cell periphery. More mature and differentiated fibroblasts from rat of human foetal lung showed staining of reticular cytoplasmic structures corresponding to phase-dense rough endoplasmic reticulum (RER). Nucleoli were prominently stained in all cultured cells. Serum absorption with ribosomes inhibited all antibody activity but absorption with RNA or with RNase-treated ribosomes resulted only in partial inhibition. Monolayers of RNase-treated fibroblasts gave weaker staining reactions compared to control untreated cultures. These observations suggest that the autoantibody is directed against ribosomal RNA and ribosomal protein present in cytoplasmic polyribosomes, in RER and in nucleoli.
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PMID:Autoantibody to ribosomes and systemic lupus erythematosus. 700 92


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