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

---

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

Poly(A)-specific ribonuclease (PARN) is an oligomeric, processive, and cap-interacting 3' exonuclease. We have studied how the m7G(5')ppp(5')G cap structure affects the activity of PARN. It is shown that the cap has four distinct effects: (i) It stimulates the rate of deadenylation if provided in cis; (ii) it inhibits deadenylation if provided at high concentration in trans; (iii) it stimulates deadenylation if provided at low concentration in trans; and (iv) it increases the processivity of PARN when provided in cis. It is shown that the catalytic and cap binding sites on PARN are separate. The important roles of the 7-methyl group and the inverted guanosine residue of the cap are demonstrated. An active deadenylation complex, consisting of the poly(A)-tailed RNA substrate and PARN, has been identified. Complex formation does not require a cap structure on the RNA substrate. The multiple effects of cap are all accounted for by a simple, kinetic model that takes the processivity of PARN into account.
...
PMID:The mRNA cap structure stimulates rate of poly(A) removal and amplifies processivity of degradation. 1135 75

Poly(A)-specific ribonuclease (PARN) is the only mammalian exoribonuclease characterized thus far with high specificity for degrading the mRNA poly(A) tail. PARN belongs to the RNase D family of nucleases, a family characterized by the presence of four conserved acidic amino acid residues. Here, we show by site-directed mutagenesis that these residues of human PARN, i.e. Asp(28), Glu(30), Asp(292), and Asp(382), are essential for catalysis but are not required for stabilization of the PARN x RNA substrate complex. We have used iron(II)-induced hydroxyl radical cleavage to map Fe(2+) binding sites in PARN. Two Fe(2+) binding sites were identified, and three of the conserved acidic amino acid residues were important for Fe(2+) binding at these sites. Furthermore, we show that the apparent dissociation constant ((app)K(d)) values for Fe(2+) binding at both sites were affected in PARN polypeptides in which the conserved acidic amino acid residues were substituted to alanine. This suggests that these residues coordinate divalent metal ions. We conclude that the four conserved acidic amino acids are essential residues of the PARN active site and that the active site of PARN functionally and structurally resembles the active site for 3'-exonuclease domain of Escherichia coli DNA polymerase I.
...
PMID:Identification of the active site of poly(A)-specific ribonuclease by site-directed mutagenesis and Fe(2+)-mediated cleavage. 1174 7

Nonsense-mediated mRNA decay (NMD) is a mechanism by which cells recognize and degrade mRNAs that prematurely terminate translation. To date, the polarity and enzymology of NMD in mammalian cells is unknown. We show here that downregulating the Dcp2 decapping protein or the PM/Scl100 component of the exosome (1) significantly increases the abundance of steady-state nonsense-containing but not nonsense-free mRNAs, and (2) significantly slows the decay rate of transiently induced nonsense-containing but not nonsense-free mRNA. Downregulating poly(A) ribonuclease (PARN) also increases the abundance of nonsense-containing mRNAs. Furthermore, NMD factors Upf1, Upf2, and Upf3X coimmunopurify with the decapping enzyme Dcp2, the putative 5'-->3' exonuclease Rat1, the proven 5'-->3' exonuclease Xrn1, exosomal components PM/Scl100, Rrp4, and Rrp41, and PARN. From these and other data, we conclude that NMD in mammalian cells degrades mRNAs from both 5' and 3' ends by recruiting decapping and 5'-->3' exonuclease activities as well as deadenylating and 3'-->5' exonuclease activities.
...
PMID:Nonsense-mediated mRNA decay in mammalian cells involves decapping, deadenylating, and exonucleolytic activities. 1452

Deadenylation is the first and rate-limiting step in the degradation of many mRNAs in a wide-range of organisms from yeast to higher eukaryotes. It can also play a regulatory role in early development. In this study, we examined the Arabidopsis homolog of poly(A) ribonuclease (PARN), a deadenylase first identified in mammals and absent from yeast. Consistent with the conservation of domains and residues important for catalytic activity, Arabidopsis PARN (AtPARN) expressed in Escherichia coli has poly(A) degradation activity in vitro. Protein localization experiments in plant cells indicate that AtPARN resides in both the nucleus and cytoplasm. To address the importance of the enzyme in vivo, we identified three independent T-DNA insertion mutants of AtPARN which interrupt the gene at different positions between the ATG and the stop codon. All three alleles cause lethality prior to seed germination, indicating that AtPARN is an essential gene first required during early development. Although homologous genes have yet to be inactivated in any other organism, our observations argue for the critical importance of PARN and suggest that it may be essential in many other multicellular eukaryotes.
...
PMID:AtPARN is an essential poly(A) ribonuclease in Arabidopsis. 1501 88

Inherently unstable mRNAs contain AU-rich elements (AREs) in their 3' untranslated regions that act as mRNA stability determinants by interacting with ARE binding proteins (ARE-BPs). The mechanisms underlying the function of ARE and ARE-BP interactions in promoting mRNA decay are not fully understood. Here, we demonstrate that KSRP, a KH domain-containing ARE-BP, is an essential factor for ARE-directed mRNA decay. Some of the KH motifs (KHs) of KSRP directly mediate RNA binding, mRNA decay, and interactions with the exosome and poly(A) ribonuclease (PARN). The ability of KHs to promote mRNA decay correlates with their ability to bind the ARE and associate with RNA-degrading enzymes. Thus, KHs promote rapid mRNA decay by recruiting degradation machinery to ARE-containing mRNAs.
...
PMID:A KH domain RNA binding protein, KSRP, promotes ARE-directed mRNA turnover by recruiting the degradation machinery. 1517 53

Deadenylation of mRNA is often the first and rate-limiting step in mRNA decay. PARN, a poly(A)-specific 3' --> 5' ribonuclease which is conserved in many eukaryotes, has been proposed to be primarily responsible for such a reaction, yet the importance of the PARN function at the whole-organism level has not been demonstrated in any species. Here, we show that mRNA deadenylation by PARN is essential for viability in higher plants (Arabidopsis thaliana). Yet, this essential requirement for the PARN function is not universal across the phylogenetic spectrum, because PARN is dispensable in Fungi (Schizosaccharomyces pombe), and can be at least severely downregulated without any obvious consequences in Metazoa (Caenorhabditis elegans). Development of the Arabidopsis embryos lacking PARN (AtPARN), as well as of those expressing an enzymatically inactive protein, was markedly retarded, and ultimately culminated in an arrest at the bent-cotyledon stage. Importantly, only some, rather than all, embryo-specific transcripts were hyperadenylated in the mutant embryos, suggesting that preferential deadenylation of a specific select subset of mRNAs, rather than a general deadenylation of the whole mRNA population, by AtPARN is indispensable for embryogenesis in Arabidopsis. These findings indicate a unique, nonredundant role of AtPARN among the multiple plant deadenylases.
...
PMID:mRNA deadenylation by PARN is essential for embryogenesis in higher plants. 1524 30

Poly(A)-specific ribonuclease (PARN) is a highly poly(A)-specific 3'-exoribonuclease that efficiently degrades mRNA poly(A) tails. PARN belongs to the DEDD family of nucleases, and four conserved residues are essential for PARN activity, i.e. Asp-28, Glu-30, Asp-292, and Asp-382. Here we have investigated how catalytically important divalent metal ions are coordinated in the active site of PARN. Each of the conserved amino acid residues was substituted with cysteines, and it was found that all four mutants were inactive in the presence of Mg2+. However, in the presence of Mn2+, Zn2+, Co2+, or Cd2+, PARN activity was rescued from the PARN(D28C), PARN(D292C), and PARN(D382C) variants, suggesting that these three amino acids interact with catalytically essential metal ions. It was found that the shortest sufficient substrate for PARN activity was adenosine trinucleotide (A3) in the presence of Mg2+ or Cd2+. Interestingly, adenosine dinucleotide (A) was efficiently hydrolyzed in the presence of Mn2+, Zn2+, or Co2+, suggesting that the substrate length requirement for PARN can be modulated by the identity of the divalent metal ion. Finally, introduction of phosphorothioate modifications into the A substrate demonstrated that the scissile bond non-bridging phosphate oxygen in the pro-R position plays an important role during cleavage, most likely by coordinating a catalytically important divalent metal ion. Based on our data we discuss binding and coordination of divalent metal ions in the active site of PARN.
...
PMID:Coordination of divalent metal ions in the active site of poly(A)-specific ribonuclease. 1535 88

Poly(A)-specific ribonuclease (PARN) is a processive, poly(A)-specific 3' exoribonuclease. The crystal structure of C-terminal truncated human PARN determined in two states (free and RNA-bound forms) reveals that PARNn is folded into two domains, an R3H domain and a nuclease domain similar to those of Pop2p and epsilon186. The high similarity of the active site structures of PARNn and epsilon186 suggests that they may have a similar catalytic mechanism. PARNn forms a tight homodimer, with the R3H domain of one subunit partially enclosing the active site of the other subunit and poly(A) bound in a deep cavity of its nuclease domain in a sequence-nonspecific manner. The R3H domain and, possibly, the cap-binding domain are involved in poly(A) binding but these domains alone do not appear to contribute to poly(A) specificity. Mutations disrupting dimerization abolish both the enzymatic and RNA-binding activities, suggesting that the PARN dimer is a structural and functional unit. The cap-binding domain may act in concert with the R3H domain to amplify the processivity of PARN.
...
PMID:Structural insight into poly(A) binding and catalytic mechanism of human PARN. 1628 Oct 54

The rate of mRNA turnover is an important determinant of levels of gene expression. Although this process has been studied extensively in mammalian cells and yeast, relatively little is known about the mRNA decay pathways in insects. Our analysis found that the vast majority of components of the mRNA decay machinery are conserved between humans and mosquitoes. Moreover, the half-lives of Aedes albopictus mRNAs are within a similar range to those of mammalian mRNAs. In order to investigate mechanistic aspects of mRNA decay in mosquitoes, we developed an in vitro system using cytoplasmic S100 extracts from A. albopictus C6/36 cells. Using this decay assay, we show here that all the pathways of mRNA turnover that have been observed in mammalian cells (deadenylation, decapping, 3'-to-5' exonucleolytic decay and 5'-to-3' exonucleolytic decay) are active in C6/36 extracts. Finally, we present compelling evidence that the major deadenylase in C6/36 extracts is likely to be a homolog of the human poly(A) specific ribonuclease, PARN. Our results suggest a high level of conservation in the factors and pathways of mRNA decay between mosquitoes and humans.
...
PMID:A cell-free mRNA stability assay reveals conservation of the enzymes and mechanisms of mRNA decay between mosquito and mammalian cell lines. 1629 Oct 88

Poly(A)-specific ribonuclease (PARN) is a cap-interacting and poly(A)-specific 3'-exoribonuclease. Here we have investigated how the cap binding complex (CBC) affects human PARN activity. We showed that CBC, via its 80-kDa subunit (CBP80), inhibited PARN, suggesting that CBC can regulate mRNA deadenylation. The CBC-mediated inhibition of PARN was cap-independent, and in keeping with this, the CBP80 subunit alone inhibited PARN. Our data suggested a new function for CBC, identified CBC as a potential regulator of PARN, and emphasized the importance of communication between the two extreme ends of the mRNA as a key strategy to regulate mRNA degradation. Based on our data, we have proposed a model for CBC-mediated regulation of PARN, which relies on an interaction between CBP80 and PARN. Association of CBC with PARN might have importance in the regulated recruitment of PARN to the nonsense-mediated decay pathway during the pioneer round of translation.
...
PMID:Inhibition of mRNA deadenylation by the nuclear cap binding complex (CBC). 1631 9


1 2 3 4 5 Next >>

---