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:3.1.13.1 (exoribonuclease)
732 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We review recent evidence on the in vivo and in vitro mRNA degradation properties of 2 3'-exonucleases, ribonuclease II and polynucleotide phosphorylase. Although secondary structures in the RNA can act as protective barriers against 3' exonucleolytic degradation, it appears that this effect depends on the stability of these structures. The fact that RNase II is more sensitive to RNA secondary structure than PNPase, could account for some differences observed in messenger degradation by the 2 enzymes in vivo. Terminator stem-loop structures are often very stable and 3' exonucleolytic degradation proceeds only after they have been eliminated by an endonucleolytic cleavage. Other secondary structures preceding terminator stem-loop seem to contribute to mRNA stability against exonucleolytic decay.
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PMID:Different specificities of ribonuclease II and polynucleotide phosphorylase in 3'mRNA decay. 208 42

The acid RNase activity of mouse liver cytosol has been resolved into two different enzymes named acid RNase I and acid RNase II respectively. Acid RNase I is a typical pancreatic-type enzyme hydrolyzing CpN and UpN bonds. Acid RNase II, however, hydrolyzes GpN bonds in non-hydrogen-bonded regions of the substrate.
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PMID:A guanyloribonuclease of mouse liver cytosol. 211 4

T. brucei cytoplasmic calcium-dependent alkaline ribonuclease activity from DEAE-cellulose fractionation was separated into endoribonuclease and exoribonuclease activities by hydroxyapatite chromatography. T. brucei cytoplasmic extract markedly decreased the endoribonuclease activity, but slightly potentiated the activities of the exoribonuclease and bovine ribonuclease A. While the endoribonuclease was activated by trypsin, the exoribonuclease and bovine ribonuclease A were partially inactivated by trypsin. The endoribonuclease was activated by p-chloromercuribenzoate or N-ethylmaleimide; the exoribonuclease was not affected by these sulfhydryl group reagents. Free ribonuclease was separated from the latent endoribonuclease by 1 M NaCl-Sephadex G-100 gel filtration. The results demonstrate that T. brucei cytoplasm contains a latent endoribonuclease consisting of ribonuclease and inhibitor protein.
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PMID:Trypanosoma brucei: calcium-dependent endoribonuclease is associated with inhibitor protein. 222 4

The isolation of a temperature-sensitive allele of RNase II (rnb) by in vitro mutagenesis has permitted the demonstration that RNase II and polynucleotide phosphorylase (PNPase) are required for cell viability and mRNA turnover in Escherichia coli. Double-mutant strains carrying the pnp-7 and rnb-500 alleles (PNPase deficient and RNase II thermolabile) ceased growing in Luria broth within 30 min after shift to the nonpermissive temperature. Cessation of growth was accompanied by an accumulation of mRNA fragments 100-1500 nucleotides long. In contrast, single-mutant and wild-type control strains grew normally at the nonpermissive temperature and did not accumulate mRNA. No significant changes in rRNA patterns were observed in any of the strains.
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PMID:Polynucleotide phosphorylase and ribonuclease II are required for cell viability and mRNA turnover in Escherichia coli K-12. 241 33

An exoribonuclease that hydrolyzes single-stranded RNA by a 5'----3' mode yielding 5'-mononucleotides has been purified from human placental nuclei. Chromatographic studies of crude placental nuclear extracts suggest that the enzyme is a relatively abundant nuclear RNase. Poly(A) is degraded by a processive mechanism while rRNA is degraded in a partially non-processive manner, possibly because of its secondary structure. The enzyme has an apparent molecular weight of 113,000, derived from determinations of the Stokes radius (43 A) and sedimentation coefficient (6.3 S). Substrates with 5'-phosphomonoester end groups are 10-20 times better than 5'-dephosphorylated substrates. The locale of the enzyme in nuclei of normal human cells as well as its mode of action suggest a role in nuclear RNA processing or turnover.
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PMID:A 5'----3' exoribonuclease of human placental nuclei: purification and substrate specificity. 243 25

We have analysed by S1 nuclease mapping the in vivo termination sites of transcription of the caa-cal operon and cai gene. The termination region for caa mRNA (T1A terminator) features characteristics of a rho-independent terminator. This terminator is a convergent transcription terminator, its complementary secondary structure being present at the 3'-end of cai mRNA. The caa-cal mRNA terminator (T2A terminator) has a stable potential secondary structure and shows homology with rho-dependent terminators. In vitro transcription of caa-cal operon demonstrated that the two terminators T1A and T2A are efficient. The 3'-ends of the mRNAs which end at T1A and T2A were analysed by S1 mapping with total RNA purified from a mutant strain deficient in exoribonuclease activities, in particular RNase II. The results suggest that the potential secondary structures of T1A and T2A are sufficiently stable to prevent 3'-end degradation by RNase II. On the other hand, the T2A terminator should be efficient enough to stop transcription through the downstream DNA region involved in pColA replication.
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PMID:Transcriptional terminators in the caa-cal operon and cai gene. 245 41

The degradation of mRNA in Escherichia coli is thought to occur through a series of endonucleolytic and exonucleolytic steps. By constructing a series of multiple mutants containing the pnp-7 (polynucleotide phosphorylase), rnb-500 (RNase II), and ams-1 (altered message stability) alleles, it was possible to study general mRNA turnover as well as the degradation of specific mRNAs. Of most interest was the ams-1 pnp-7 rnb-500 triple mutant in which the half-life of total pulse-labeled RNA increased three- to fourfold at the nonpermissive temperature. RNA-DNA hybridization analysis of several specific mRNAs such as trxA (thioredoxin), ssb (single-stranded-DNA-binding protein), uvrD (DNA helicase II), cat (chloramphenicol acetyltransferase), nusA (N utilization substance), and pnp (polynucleotide phosphorylase) demonstrated two- to fourfold increases in their chemical half-lives. A new method for high-resolution Northern (RNA) analysis showed that the trxA and cat mRNAs are degraded into discrete fragments which are significantly stabilized only in the triple mutant. A model for mRNA turnover is discussed.
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PMID:Stabilization of discrete mRNA breakdown products in ams pnp rnb multiple mutants of Escherichia coli K-12. 245 6

Highly purified and commercially available preparations of reverse transcriptases from retroviruses contain a 3' to 5' exoribonuclease activity capable of hydrolyzing synthetic homopolyribonucleotides having a 3'-OH end. The exoribonuclease activity of reverse transcriptase preparations from Rous associated virus-2 was further characterized. This exoribonuclease activity cleaves poly(C) and poly(U) exonucleolytically from the 3'-OH end to produce nucleoside 5'-phosphates. Poly(A), poly(G), circular polyribonucleotide, and double-stranded polyribonucleotide were not hydrolyzed by the activity. This is a novel type of exoribonuclease activity.
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PMID:Exoribonuclease activity of purified reverse transcriptase preparations from retroviruses. 247 86

We have characterized a chloroplast processing activity that catalyzes the conversion of the plastid cytochrome b6/f subunit IV (pet D) mRNA 3' end precursor to the mature RNA possessing a 3' inverted repeat (IR). In a chloroplast soluble protein extract, the activity requires Mg2+ or Mn2+, but not K+. In the absence of Mg2+, the pet D 3' IR-RNA product does not accumulate, and UV-cross-linking indicates that the 3' IR-RNA precursor binds several new proteins in addition to those previously characterized as part of the 3' IR-RNA: protein complex in vitro. In contrast, high concentrations of Zn2+ or Cu2+ suppress protein binding and inhibit the processing reaction. The purified exoribonuclease polynucleotide phosphorylase (E.C.2.7.7.8) is not efficient in processing the pet D 3' IR-RNA precursor, whereas Escherichia coli ribonuclease II rapidly processes the pet D IR-RNA precursor to a product of a size similar to that of the mature 3' IR-RNA, but also rapidly degrades the mature RNA in the absence of chloroplast extract. We therefore conclude that the maturation of the pet D mRNA in vitro requires specific chloroplast enzymes which process the mRNA 3' end precursor in the absence of efficient transcription termination. The chloroplast enzyme activities are biochemically distinct from their bacterial counterparts. We also note that specific chloroplast components may be required to stabilize the mature pet D mRNA 3' end against further exonucleolytic degradation.
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PMID:Chloroplast mRNA 3' end maturation is biochemically distinct from prokaryotic mRNA processing. 248 89

Previous studies on regulation of the spc operon containing genes for ribosomal proteins have shown that S8, encoded by the fifth gene of the operon in Escherichia coli, is a translational repressor and regulates the synthesis of the third gene product (L5) and distal gene products by acting at a site near the L5 mRNA translation initiation site. We have now shown that S8 also regulates the synthesis of the first and second gene products (L14 and L24) of the operon by acting at the same mRNA target site--that is, the site located distal to sites coding for L14 and L24--and that mRNA degradation is involved in this retroregulation. It was shown that single base substitutions in the target site, which abolish repression of the synthesis of L5 and L5-distal gene products by S8, also cause derepression of L14-L24 synthesis. Inhibition of L14-L24 synthesis by S8 was also shown by overproducing S8 in trans from a plasmid carrying the S8 gene under lac promoter/operator control. A strain carrying temperature-sensitive mutations in genes for polynucleotide phosphorylase and RNase II was found upon shift to nonpermissive temperature to show higher differential synthesis rates of L14-L24 (and L5) relative to those of several L5-distal spc operon gene products. We suggest that repression of distal ribosomal protein synthesis by S8 triggers nucleolytic cleavage of spc operon mRNA, followed by mRNA degradation by these 3'- to 5'- exonucleases, which is then responsible for inhibition of L14-L24 synthesis.
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PMID:Retroregulation of the synthesis of ribosomal proteins L14 and L24 by feedback repressor S8 in Escherichia coli. 264 12


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