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 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

In a temperature-sensitive mutant of E. coli defective in tRNA biosynthesis, many tRNA precursors, including monomeric and multimeric forms, accumulate. Some of the multimeric precursors contain three or more tRNA sequences within a molecule. These large precursors were cleaved by cell extracts first into intermediate size pieces which were subsequently processed by RNase P. On the basis of heat stability of mutant cell extracts, the endonuclease responsible for the initial cleavage appears to be distinct from RNase P and is designated RNase O. One of the monomeric precursors was shown to be processed first by RNase P and the product subsequently cleaved further into a smaller molecule. The nuclease responsible for this second cleavage also appears to be distinct from RNase P and is designated RNase Q. The functions of these nucleases are sequential in the trimming process with respect to that of RNase P; RNase O works prior to RNase P and RNase Q after RNase P but in both cases, not vice versa.
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PMID:Sequential processing of precursor tRNA molecules in Escherichia coli. 110 44

Our results indicate that RNase P has a very general role in the processing of tRNA precursors in E. coli, being responsible for the cleavage of virtually all precursor molecules at a site corresponding to the 5' end of the mature tRNA, and that at least two other RNases play specific roles in precursor processing. One of these, which may be RNase II, is responsible for removing extra nucleotides from the 3' end of tRNA precursors. The other, which we call RNase P2, is an endonuclease that cleaves precursors in spacer regions between different tRNA sequences; this enzyme is involved in the processing of large multimeric precursors.
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PMID:Processing of E. coli tRNA precursors. 110

f2 phage RNA treated with O-methylhydroxylamine under denaturing conditions loses its ordered structure with consequent exposure of the normally hidden initiation codons. In the presence of Escherichia coli ribosomes and crude initiation factors modified f2 RNA binds about 50 times more f-[3H]Met-tRNA than native f2 RNA. The interaction of native f2[14C]RNA with ribosomes requires initiation factors. The binding of O-methylhydroxylamine-modified f2 [14C]RNA to E. coli 70-S or 20-S ribosomes does not depend on the presence of initiation factors. A significant number of ribosomes deficient in initiation factors interact with a molecule of modified f2 [14C]RNA. Treatment of the resultant polysomal complex with pancreatic RNase yields ribosomes with f2 RNA fragments protected against RNase. Almost all AUG/GUG codons in the f2 RNA are located on the RNase-insensitive ribosome-bound fragments, constituting only 25% of the entire molecule. Addition of crude initiation factors to such ribosomes with fragments of modified f2 RNA promotes binding of f-[3H]Met-tRNA. The resultant complex is fully reactive with puromycin. No binding of Ac-Phe-tRNA takes place under similar conditions.
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PMID:Recognition of initiation codons in modified f2 RNA by Escherichia coli ribosomes. 110 35

tRNA-tDNA hybrids from yeast have been isolated. The main step in purification was chromatography on a BD-cellulose column with salt gradients and formamide, which separates the hybrid material from excess DNA. The hybrids were characterized by density centrifugation in CS2SO4 and by treatment with alkali and pancreatic ribonuclease. Experiments in which DNA that had been sheared to different molecular weights was used for hybrid formation suggest that the tRNA cistrons are tandemly arranged and that the external spacer DNA is preserved in the tDNA.
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PMID:Purification of tDNA from yeast. 110 99

A procedure for the preparation of a large quantity of biologically active, highly purified ribosomes from rabbit liver is described. The method employs polyethylene glycol-dextran sulfate parition and DEAE-cellulose chromatography to overcome the limitations encountered in conventional procedures. The entire process takes only 48 h to obtain 10,000 A(260) units of ribosomes. The ribosomes thus obtained are predominantly 78S particles with a constant protein-RNA ratio of 0.95. The ribosomes are free from RNase, amino-acyl-tRNA synthetase, and amino-acyl-tRNA: protein transferase activity. The protein synthesizing activity is dependent on added mRNA and protein factors. These ribosomes are stable for prolonged periods of storage in a liquid nitrogen refrigerator.
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PMID:Cell-free protein synthesis in t,e rabbit liver ribosomal system. II. Large scale preparation of purified 80S ribosomes. 113 93

The major form of methionine tRNA operational in the elongation of protein synthesis in mouse myeloma cells was purufied from these cells after they had been cultured in the presence of [32P]-phosphate. This [32P]tRNA4-Met species was then digested with T1 RNase or pancreatic RNase so as to obtain both complete and partial RNase digestion products. The nucleotide sequences of these fragments were analysed to enable the derivation of the complete primary structure of this tRNA. tRNA4-Met of mouse myeloma cells is 76 nucleotides in length and contains 15 modified nucleotides. It is the only tRNA yet sequenced which has been found to possess the minor nucleoside 2-methylguanosine (m2G) within the amino acid (a) stem, and also to have an anticodon (c) stem of only 4 and not 5 base-pairs. The loop IV sequence of eukaryotic initiator methionine tRNA (tRNAf-Met) species, -A-U-C-G-m1A-A-A-, IS NOT FOUND IN TRNA4-Met and is therefore absent from at least one of the methionine tRNAs functioning in polypeptide elongation in mammalian cells. This is consistent with the suggested importance of this loop structure in the initiator function of tRNAf-Met in eukaryotic organisms. Three distinct regions of the tRNA cloverleaf, the (b) stem, the anticodon loop (loop II), and loop III, are substantially conserved in structure between tRNAf-Met and tRNA4-Met of mouse myeloma cells. These regions of the structures of mammalian methionine tRNAs probably do not determine whether a certain tRNA-Met will function in the initiation or elongation of protein synthesis, although they might be important in tRNA-Met recognition if the different cytoplasmic tRNA-Met species of mammalian cells are aminoacylated by a single activating enzyme.
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PMID:The nucleotide sequence of a methionine tRNA which functions in protein elongation in mouse myeloma cells. 116 34

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

Studies were conducted on the stimulatory effect that various nucleic-acid-binding compounds have on the hydrolysis of RNA and polyribonucleotides by pancreatic ribonuclease A and by other ribonucleases. The stimulatory activity of chloroquine on tRNA hydrolysis by pancreatic ribonuclease was due to the formation of oligonucleotides of a wide range of sizes and was not due to the formation of very short ( n greater than 5) oligonucleotide fragments of tRNA. The dextrorotatory and levorotatory isomers of chloroquine did not differ in their ability to stimulate the hydrolysis of tRNA by pancreatic ribonuclease A. In addition to chloroquine and primaquine, other nucleic-acid-binding compounds (e.g., quinacrine, lucanthone, and proflavin) stimulated the hydrolysis of tRNA by pancreatic ribonuclease A. Chloroquine did not alter the rate of hydrolysis by pancreatic ribonuclease A of low-molecular-weight substrates (cytidine cyclic 2':o'-monophosphate, uridine cyclic 2':3'-monophosphate, cytidylyl-adenosine, or uridylyl-uridine). Furthermore, chloroquine and primaquine did not affect the hydrolysis of poly(A) by high concentrations of pancreatic ribonuclease A. In studies on the hydrolysis of tRNA by other endoribonucleases, several of the nucleic-acid-binding compounds (e.g., quinacrine and ethidium) exhibited appreciable inhibition of both ribonuclease N1 and ribonuclease T1. None of the compounds tested stimulated the activity of ribonuclease T1, and only chloroquine, and perhaps lucanthone, stimulated the hydrolysis of tRNA by ribonuclease N1.
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PMID:Effect of nucleic-acid-binding compounds on the hydrolytic activity of various ribonucleases. 120 47

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


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