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Google, Apple and Microsoft : study of competitive strategies in the early 21st century software industry

Boff, Felipe de Moraes
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Trabalho de Conclusão de Curso Formato: application/pdf
ENG
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This work reviews the very brief history of the software industry, dividing it into three types of products — software contractors, corporate software products, and massmarket software. Here I demonstrate that mass-market software producers face an oligopolistic market, and I ask whether static oligopoly theory is suitable to analyse behaviour of firms when producing an operating system. Therefore, throughout this work, I formally analyse the strategic competition for market share, concerning three touchstone models of oligopoly theory— Cournot, Bertrand, and Stackelberg’s. Google, Apple, and Microsoft produced, in the early 21st century, mobile operating systems that are perfect substitutes. However, in their advertisements, these three giant mass-market software producers signalise their products as dissimilar. This work demonstrates that the core functions and performance of these operating systems are indeed very alike, and that consumers make purchase decisions considering the perceived quality as a variable of choice. With these results, I describe hypothetical strategic behaviour of the producers and their unfolding results.; Este trabalho analisa uma breve história da indústria de software dividindo-a em três tipos de empresas — desenvolvedoras de custom-software...

Energy substrate used by workers of leaf-cutting ants during nest excavation

Camargo, Roberto S.; Lopes, Juliane F. S.; Forti, Luiz C.; Somera, Alexandre F.; Bacci Jr, Mauricio
Fonte: Sociedade Brasileira de Entomologia Publicador: Sociedade Brasileira de Entomologia
Tipo: Artigo de Revista Científica Formato: 397-400
ENG
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Energy substrate used by workers of leaf-cutting ants during nest excavation. In this study we aimed to ascertain whether leaf-cutting ant workers lose body reserves (fat or sugars) as a function of nest excavation. For each treatment, we isolated 10 workers of Atta sexdens into two experimental groups, Control (C- without excavation) and Soil (S- with excavation), which were kept for different time intervals (0, 24, 48 or 72 hours), totaling 700 tested workers. We then determined the concentration of soluble carbohydrates and total lipid content in them. The total carbohydrates were determined colorimetrically, based on the reaction between carbohydrates and sulfuric acid-phenol. For determination of lipids, the insects were immersed in organic solvent until they reached a constant weight. Our results showed that carbohydrates are consumed during nest excavation activities. In the experimental groups S24, S48 and S72, there was an average reduction of 5.82 (20.42%), 14.31 (44.96%) and 13.27 (43.96%) µ.mg-1 in soluble sugar when compared with the experimental groups that did not excavate. Furthermore, the lipids were not used during this activity. With respect to dry mass of the workers, their values were C0 = 8%, C24 = 10.4%, C48 = 9.2%...

Energy substrate used by workers of leaf-cutting ants during nest excavation

Camargo,Roberto S.; Lopes,Juliane F. S.; Forti,Luiz C.; Somera,Alexandre F.; Bacci Jr,Mauricio
Fonte: Sociedade Brasileira De Entomologia Publicador: Sociedade Brasileira De Entomologia
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2013 EN
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Energy substrate used by workers of leaf-cutting ants during nest excavation. In this study we aimed to ascertain whether leaf-cutting ant workers lose body reserves (fat or sugars) as a function of nest excavation. For each treatment, we isolated 10 workers of Atta sexdens into two experimental groups, Control (C- without excavation) and Soil (S- with excavation), which were kept for different time intervals (0, 24, 48 or 72 hours), totaling 700 tested workers. We then determined the concentration of soluble carbohydrates and total lipid content in them. The total carbohydrates were determined colorimetrically, based on the reaction between carbohydrates and sulfuric acid-phenol. For determination of lipids, the insects were immersed in organic solvent until they reached a constant weight. Our results showed that carbohydrates are consumed during nest excavation activities. In the experimental groups S24, S48 and S72, there was an average reduction of 5.82 (20.42%), 14.31 (44.96%) and 13.27 (43.96%) µ.mg-1 in soluble sugar when compared with the experimental groups that did not excavate. Furthermore, the lipids were not used during this activity. With respect to dry mass of the workers, their values were C0 = 8%, C24 = 10.4%, C48 = 9.2%...

Caracterização morfológica e dissimilaridade genética entre variedades crioulas de melão

Neitzke,Raquel Silviana; Barbieri,Rosa Lía; Heiden,Gustavo; Büttow,Miriam V; Oliveira,Clarisse S; Corrêa,Lauís B; Schwengber,José Ernani; Carvalho,Fernando IF de
Fonte: Associação Brasileira de Horticultura Publicador: Associação Brasileira de Horticultura
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2009 PT
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Variedades crioulas de melão (Cucumis melo) são cultivadas no Sul do Brasil para consumo familiar e também para comercialização dos frutos. No entanto, existe uma carência de trabalhos relativos a sua caracterização. Este trabalho teve por objetivo caracterizar e avaliar a variabilidade genética de variedades crioulas de melão do Sul do Brasil mantidos no Banco Ativo de Germoplasma de Cucurbitáceas da Embrapa Clima Temperado. Foram caracterizados 14 acessos utilizando 26 descritores morfológicos de fruto. Os dados foram analisados pelos métodos de agrupamento de Tocher e hierárquico UPGMA. Os métodos de agrupamento foram parcialmente concordantes. O acesso C88 possui características distintas, ficando isolado dos demais, pois é o único entre todos os avaliados que apresenta formato piriforme e sem gomos, cor de epicarpo creme, cor de polpa branca e ruptura profunda no fruto. Existe grande variabilidade genética, para caracteres de frutos, nas variedades crioulas de melão conservadas nesse Banco Ativo de Germoplasma, com potencial para uso no melhoramento genético, destacando-se o acesso C71 por possuir sabor adocicado e polpa de cor laranja e o C72, por apresentar elevados valores de peso de fruto e espessura de polpa.

Species-specific differences in the operational RNA code for aminoacylation of tRNATrp

Xu, Feng; Chen, Xianglong; Xin, Li; Chen, Li; Jin, Youxin; Wang, Debao
Fonte: Oxford University Press Publicador: Oxford University Press
Tipo: Artigo de Revista Científica
Publicado em 15/10/2001 EN
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Identity elements play essential roles in the recognition of tRNAs by their cognate aminoacyl-tRNA synthetase. An operational RNA code relates amino acids to specific sequences and structural features of tRNA acceptor stems. In this study, a series of tRNATrp variants was prepared by in vitro transcription and their efficiencies of aminoacylation by tryptophan (kcat/Km) were measured with the aid of Bacillus subtilis and human tryptophanyl-tRNA synthetases (TrpRS). The identity elements in the operational RNA code of human tRNATrp were found to be: major element, discriminator base A73; minor elements, G1/C72 and U5/G68. From the cross-species aminoacylation assays, we conclude that the identity elements in tRNATrp from B.subtilis and human all contribute to species-specific aminoacylation by TrpRS. Analyses of 22 TrpRS sequences covering three taxonomic domains (bacteria, eukarya and archaea) reveal that the sequences are divided into two evolutionarily distant groups. The same partition is also observed in the analyses of tRNATrp acceptor stem sequences. Our data suggest that the two TrpRS groups may reflect co-adaptations needed to accommodate changes in the operational RNA code for tryptophan.

Initiator-Elongator Discrimination in Vertebrate tRNAs for Protein Synthesis

Drabkin, Harold J.; Estrella, Melanie; Rajbhandary, Uttam L.
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /03/1998 EN
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Initiator tRNAs are used exclusively for initiation of protein synthesis and not for the elongation step. We show, in vivo and in vitro, that the primary sequence feature that prevents the human initiator tRNA from acting in the elongation step is the nature of base pairs 50:64 and 51:63 in the TΨC stem of the initiator tRNA. Various considerations suggest that this is due to sequence-dependent perturbation of the sugar phosphate backbone in the TΨC stem of initiator tRNA, which most likely blocks binding of the elongation factor to the tRNA. Because the sequences of all vertebrate initiator tRNAs are identical, our findings with the human initiator tRNA are likely to be valid for all vertebrate systems. We have developed reporter systems that can be used to monitor, in mammalian cells, the activity in elongation of mutant human initiator tRNAs carrying anticodon sequence mutations from CAU to CCU (the C35 mutant) or to CUA (the U35A36 mutant). Combination of the anticodon sequence mutation with mutations in base pairs 50:64 and 51:63 yielded tRNAs that act as elongators in mammalian cells. Further mutation of the A1:U72 base pair, which is conserved in virtually all eukaryotic initiator tRNAs, to G1:C72 in the C35 mutant background yielded tRNAs that were even more active in elongation. In addition...

Structure of the acceptor stem of Escherichia coli tRNA Ala: role of the G3.U70 base pair in synthetase recognition.

Ramos, A; Varani, G
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 01/06/1997 EN
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The fidelity of translation of the genetic code depends on accurate tRNA aminoacylation by cognate aminoacyl-tRNA synthetases. Thus, each tRNA has specificity not only for codon recognition, but also for amino acid identity; this aminoacylation specificity is referred to as tRNA identity. The primary determinant of the acceptor identity of Escherichia coli tRNAAlais a wobble G3.U70 pair within the acceptor stem. Despite extensive biochemical and genetic data, the mechanism by which the G3.U70 pair marks the acceptor end of tRNAAla for aminoacylation with alanine has not been clarified at the molecular level. The solution structure of a microhelix derived from the tRNAAla acceptor end has been determined at high precision using a very extensive set of experimental constraints (approximately 32 per nt) obtained by heteronuclear multidimensional NMR methods. The tRNAAla acceptor end is overall similar to A-form RNA, but important differences are observed. The G3.U70 wobble pair distorts the conformation of the phosphodiester backbone and presents the functional groups of U70 in an unusual spatial location. The discriminator base A73 has extensive stacking overlap with G1 within the G1.C72 base pair at the end of the double helical stem and the -CCA end is significantly less ordered than the rest of the molecule.

Probing structural elements in RNA using engineered disulfide cross-links.

Maglott, E J; Glick, G D
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 01/03/1998 EN
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Three analogs of unmodified yeast tRNAPhe, each possessing a single disulfide cross-link, have been designed and synthesized. One cross-link is between G1 and C72 in the amino acid acceptor stem, a second cross-link is in the central D region of yeast tRNAPhe between C11 and C25 and the third cross-link bridges U16 and C60 at the D loop/T loop interface. Air oxidation to form the cross-links is quantitative and analysis of the cross-linked products by native and denaturing PAGE, RNase T1 mapping, Pb(II) cleavage, UV cross-linking and thermal denaturation demonstrates that the disulfide bridges do not alter folding of the modified tRNAs relative to the parent sequence. The finding that cross-link formation between thiol-derivatized residues correlates with the position of these groups in the crystal structure of native yeast tRNAPhe and that the modifications do not significantly perturb native structure suggests that this methodology should be applicable to the study of RNA structure, conformational dynamics and folding pathways.

The A1 x U72 base pair conserved in eukaryotic initiator tRNAs is important specifically for binding to the eukaryotic translation initiation factor eIF2.

Farruggio, D; Chaudhuri, J; Maitra, U; RajBhandary, U L
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /08/1996 EN
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The formation of a specific ternary complex between eukaryotic initiation factor 2 (eIF2), the initiator methionyl-tRNA (Met-tRNA), and GTP is a critical step in translation initiation in the cytoplasmic protein-synthesizing system of eukaryotes. We show that the A1 x U72 base pair conserved at the end of the acceptor stem in eukaryotic and archaebacterial initiator methionine tRNAs plays an important role in this interaction. We changed the A1 x U72 base pair of the human initiator tRNA to G1 x C72 and expressed the wild-type and mutant tRNA genes in the yeast Saccharomyces cerevisiae by using constructs previously developed in our laboratory for expression of the human initiator tRNA gene in yeasts. We show that both the wild-type and mutant human initiator tRNAs are aminoacylated well in vivo. We have isolated the wild-type and mutant human initiator tRNAs in substantially pure form, free of the yeast initiator tRNA, and have analyzed their properties in vitro. The G1 x C72 mutation affects specifically the binding affinity of eIF2 for the initiator tRNA. It has no effect on the subsequent formation of 40S or 80S ribosome initiator Met-tRNA-AUG initiation complexes in vitro or on the puromycin reactivity of the Met-tRNA in the 80S initiation complex.

Identity determinants of E. coli tryptophan tRNA.

Himeno, H; Hasegawa, T; Asahara, H; Tamura, K; Shimizu, M
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 11/12/1991 EN
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The first base pair of the acceptor stem A1-U72 and the discriminator base G73, as well as the anticodon nucleotides, characterize the tryptophan tRNA in E. coli. To determine the contribution of these nucleotides to the tryptophan acceptor activity, various transcripts of E. coli tryptophan tRNA mutants were constructed. Substitutions of the discriminator base G73, which is conserved within prokaryotic tryptophan tRNAs, impaired aminoacylation with tryptophan. Substitutions of other purine-pyrimidine pairs for A1-U72 revealed that only U72 weakly contributed to recognition by tryptophanyl-tRNA synthetase. The E. coli aspartic acid tRNA transcript introducing the tryptophan anticodon CCA showed almost the same tryptophan charging activity as the tryptophan tRNA transcript possessing a G1-C72 base pair. Only a low activity was detected in the mutant tryptophan tRNA transcript possessing a set of G1-C72 and A73, which is observed in eukaryotic tryptophan tRNAs. These results indicate that the anticodon and G73 are major identity determinants of tryptophan tRNA in E. coli, whereas the A1-U72 base pair is only a weak recognition element.

LL-A491, A Monazomycin-like Antibiotic

Mitscher, Lester A.; Shay, Anthony J.; Bohonos, Nestor
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /09/1967 EN
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A new antibiotic, designated LL-A491, was isolated by butanol extraction and crystallization from beers of an unidentified streptomycete, Lederle culture A491. LL-A491 was primarily active against gram-positive bacteria and was related to monazomycin. A tentative molecular formula of C72±2 H144±8 O25±1 N for the antibiotic, based on analyses of the crystalline hydrochloride, picrate, and picrolonate salts, is considerably larger than that proposed for monazomycin, from which LL-A491 was not differentiated by paper chromatography. Analysis of the amorphous polyacetate ester suggested 15 to 16 acetylable groups. Upon hydrolysis, LL-A491 liberated ammonia and a reducing sugar which appeared to be mannose. LL-A491 was dextrorotatory, [α]D25 + 14°, and exhibited only end absorption in the ultraviolet region.

Human mitochondrial TyrRS disobeys the tyrosine identity rules

BONNEFOND, LUC; FRUGIER, MAGALI; GIEGÉ, RICHARD; RUDINGER-THIRION, JOËLLE
Fonte: Copyright 2005 by RNA Society Publicador: Copyright 2005 by RNA Society
Tipo: Artigo de Revista Científica
Publicado em /05/2005 EN
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Human tyrosyl-tRNA synthetase from mitochondria (mt-TyrRS) presents dual sequence features characteristic of eubacterial and archaeal TyrRSs, especially in the region containing amino acids recognizing the N1-N72 tyrosine identity pair. This would imply that human mt-TyrRS has lost the capacity to discriminate between the G1-C72 pair typical of eubacterial and mitochondrial tRNATyr and the reverse pair C1-G72 present in archaeal and eukaryal tRNATyr. This expectation was verified by a functional analysis of wild-type or mutated tRNATyr molecules, showing that mt-TyrRS aminoacylates with similar catalytic efficiency its cognate tRNATyr with G1-C72 and its mutated version with C1-G72. This provides the first example of a TyrRS lacking specificity toward N1-N72 and thus of a TyrRS disobeying the identity rules. Sequence comparisons of mt-TyrRSs across phylogeny suggest that the functional behavior of the human mt-TyrRS is conserved among all vertebrate mt-TyrRSs.

Two distinct regions in Staphylococcus aureus GatCAB guarantee accurate tRNA recognition

Nakamura, Akiyoshi; Sheppard, Kelly; Yamane, Junji; Yao, Min; Söll, Dieter; Tanaka, Isao
Fonte: Oxford University Press Publicador: Oxford University Press
Tipo: Artigo de Revista Científica
EN
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In many prokaryotes the biosynthesis of the amide aminoacyl-tRNAs, Gln-tRNAGln and Asn-tRNAAsn, proceeds by an indirect route in which mischarged Glu-tRNAGln or Asp-tRNAAsn is amidated to the correct aminoacyl-tRNA catalyzed by a tRNA-dependent amidotransferase (AdT). Two types of AdTs exist: bacteria, archaea and organelles possess heterotrimeric GatCAB, while heterodimeric GatDE occurs exclusively in archaea. Bacterial GatCAB and GatDE recognize the first base pair of the acceptor stem and the D-loop of their tRNA substrates, while archaeal GatCAB recognizes the tertiary core of the tRNA, but not the first base pair. Here, we present the crystal structure of the full-length Staphylococcus aureus GatCAB. Its GatB tail domain possesses a conserved Lys rich motif that is situated close to the variable loop in a GatCAB:tRNAGln docking model. This motif is also conserved in the tail domain of archaeal GatCAB, suggesting this basic region may recognize the tRNA variable loop to discriminate Asp-tRNAAsn from Asp-tRNAAsp in archaea. Furthermore, we identified a 310 turn in GatB that permits the bacterial GatCAB to distinguish a U1–A72 base pair from a G1–C72 pair; the absence of this element in archaeal GatCAB enables the latter enzyme to recognize aminoacyl-tRNAs with G1–C72 base pairs.

Cell Cycle Arrest and Cell Survival Induce Reverse Trends of Cardiolipin Remodeling

Chao, Yu-Jen; Chang, Wan-Hsin; Ting, Hsiu-Chi; Chao, Wei-Ting; Hsu, Yuan-Hao Howard
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 25/11/2014 EN
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17.2%
Cell survival from the arrested state can be a cause of the cancer recurrence. Transition from the arrest state to the growth state is highly regulated by mitochondrial activity, which is related to the lipid compositions of the mitochondrial membrane. Cardiolipin is a critical phospholipid for the mitochondrial integrity and functions. We examined the changes of cardiolipin species by LC-MS in the transition between cell cycle arrest and cell reviving in HT1080 fibrosarcoma cells. We have identified 41 cardiolipin species by MS/MS and semi-quantitated them to analyze the detailed changes of cardiolipin species. The mass spectra of cardiolipin with the same carbon number form an envelope, and the C64, C66, C68, C70 C72 and C74 envelopes in HT1080 cells show a normal distribution in the full scan mass spectrum. The cardiolipin quantity in a cell decreases while entering the cell cycle arrest, but maintains at a similar level through cell survival. While cells awakening from the arrested state and preparing itself for replication, the groups with short acyl chains, such as C64, C66 and C68 show a decrease of cardiolipin percentage, but the groups with long acyl chains, such as C70 and C72 display an increase of cardiolipin percentage. Interestingly...

Cooperative VS. Non-cooperative Truels: Little Agreement, but Does that Matter?

BOSSERT, Walter; BRAMS, Steven J.; KILGOUR, D. Marc
Fonte: Université de Montréal Publicador: Université de Montréal
Tipo: Artigo de Revista Científica Formato: 516002 bytes; application/pdf
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It is well-known that non-cooperative and cooperative game theory may yield different solutions to games. These differences are particularly dramatic in the case of truels, or three-person duels, in which the players may fire sequentially or simultaneously, and the games may be one-round or n-round. Thus, it is never a Nash equilibrium for all players to hold their fire in any of these games, whereas in simultaneous one-round and n-round truels such cooperation, wherein everybody survives, is in both the a -core and ß -core. On the other hand, both cores may be empty, indicating a lack of stability, when the unique Nash equilibrium is one survivor. Conditions under which each approach seems most applicable are discussed. Although it might be desirable to subsume the two approaches within a unified framework, such unification seems unlikely since the two approaches are grounded in fundamentally different notions of stability.; Nous analysons des « truels » qui sont des jeux spécifiques avec trois joueurs. Il est démontré que, dans ces jeux, les résultats de la théorie des jeux non-coopératifs sont très différents des résultats qui sont obtenus en utilisant une théorie coopérative.

Markets for Information: Of Inefficient Firewalls and Efficient Monopolies

CABRALES, Antonio; GOTTARDI, Piero
Fonte: European University Institute Publicador: European University Institute
Tipo: Trabalho em Andamento Formato: application/pdf; digital
EN
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In this paper we study, within a formal model, market environments where information is costly to acquire and is of use also to potential competitors. Agents may then sell, or buy, reports over the information acquired and choose the trades in the market on the basis of what they learnt. Reports are unverifiable - cheap talk messages – hence the quality of the information transmitted depends on the conflicts of interest faced by the senders. We find that, in equilibrium, information is acquired when its costs are not too high and in that case it is also sold, though reports are typically noisy. Also, the market for information tends to be a monopoly, and there is inefficiency given by underinvestment in information acquisition. Regulatory interventions in the form of firewalls, limiting the access to the sale of information to agents uninterested in trading the underlying object, only make the inefficiency worse. Efficiency can be attained with a monopolist selling differentiated information, provided entry is blocked. The above findings hold when information has a prevalent horizontal differentiation component. When the vertical differentiation element is more important firewalls can in fact be beneficial. JEL Classification: D83...

The Ghost in the Machine: Inferring Machine-Based Strategies from Observed Behavior

ENGLE-WARNICK, Jim; McCAUSLAND, William; MILLER, John H.
Fonte: Université de Montréal Publicador: Université de Montréal
Tipo: Artigo de Revista Científica Formato: 335012 bytes; application/pdf
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We introduce a procedure to infer the repeated-game strategies that generate actions in experimental choice data. We apply the technique to set of experiments where human subjects play a repeated Prisoner's Dilemma. The technique suggests that two types of strategies underly the data.

Structural studies on tRNA acceptor stem microhelices: exchange of the discriminator base A73 for G in human tRNALeu switches the acceptor specificity from leucine to serine possibly by decreasing the stability of the terminal G1-C72 base pair.

Metzger, A U; Heckl, M; Willbold, D; Breitschopf, K; RajBhandary, U L; Rösch, P; Gross, H J
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 15/11/1997 EN
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27.2%
Correct recognition of transfer RNAs (tRNAs) by aminoacyl-tRNA synthetases (aaRS) is crucial to the maintenance of translational fidelity. The discriminator base A73 in human tRNALeuis critical for its specific recognition by the aaRS. Exchanging A73 for G abolishes leucine acceptance and converts it into a serine acceptor in vitro . Two RNA microhelices of 24 nt length that correspond to the tRNALeuacceptor stem and differ only in the discriminator base were synthesized: a wild-type tRNALeumicrohelix, where nt 21 corresponds to the discriminator base position 73, and an A21G mutant microhelix. To investigate whether different identities of both tRNAs are caused by conformational differences, NMR and UV melting experiments were performed on both microhelices. Two-dimentional NOESY spectra showed both microhelices to exhibit the same overall conformation at their 3'-CCA ends. Thermodynamic analysis and melting behaviour of the base-paired imino protons observed by NMR spectroscopy suggest that the A21G (A73G in tRNA) exchange results in a decrease of melting transition cooperativity and a destabilization of the terminal G1-C20 (G1-C72 in tRNA) base pair. Furthermore, the fact that this 3'-terminal imino proton is more solvent-exposed at physiological temperature might be another indication for the importance of the stability of the terminal base pair for specific tRNA recognition.

Site-specific deoxynucleotide substitutions in yeast U6 snRNA block splicing of pre-mRNA in vitro.

Kim, C H; Ryan, D E; Marciniec, T; Abelson, J
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 15/04/1997 EN
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We have identified 2'-hydroxyl groups of the U6 phosphate-ribose backbone which are required for reconstitution of splicing activity in U6-depleted yeast extract. To screen the 2'-hydroxyls of yeast U6 at nucleotides 39-88, spanning the conserved central domain, synthetic U6 RNAs were constructed with deoxyribonucleotides incorporated site specifically. Only four individual deoxynucleotide substitutions blocked splicing activity: dA51 (in the ACAGAG sequence), dA62 (next to the AGC triad), and dU70 and dC72 (both in the loop of the 3' intramolecular stem-loop). Native gel analysis revealed that these deoxy-substituted U6 RNAs were competent for assembly of spliceosomes. Interestingly, a 2'-O-methyl substituent at A51, A62, U70 or C72 did not inhibit splicing activity, indicating that the essential 2'-OH groups at these positions in U6 act as hydrogen bond acceptors or neutral coordinated ligands. The requisite 2'-hydroxyls at A62, U70 and C72 show both similarities and differences relative to the positions of essential 2'-hydroxyls of catalytic domain V of group II ribozymes. The identification of the essential 2'-hydroxyls at positions 62, 70 and 72 corroborates that the 3' intramolecular stem-loop in U6 plays an important role in pre-mRNA splicing.

Determination of molecular species composition of C80 or longer-chain alpha-mycolic acids in Mycobacterium spp. by gas chromatography-mass spectrometry and mass chromatography.

Kaneda, K; Naito, S; Imaizumi, S; Yano, I; Mizuno, S; Tomiyasu, I; Baba, T; Kusunose, E; Kusunose, M
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /12/1986 EN
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The molecular species composition of alpha-mycolic acids ranging from C68 to C86 in 13 rapidly growing and 12 slowly growing mycobacterial species was determined by gas chromatography, gas chromatography-mass spectrometry, and mass chromatography. In gas chromatographic analysis, the molecular species of alpha-mycolic acids were well separated as trimethylsilyl ether derivatives of the methyl esters, according to their total carbon numbers. The total carbon and double-bond numbers of mycolic acids at each peak on gas chromatograms were determined from the [M]+, [M - 15]+, and [M - 90]+ ions on the mass spectrum, and straight and branched chain structures were identified by the mass fragment ions [A]+, due to C2--C3 cleavage [R-CH-O-Si(CH3)3]+, and [B]+, due to C3--C4 cleavage [(CH3)3-Si-O-CH-CH(R')-COOCH3]+. The concentration of odd- and even-carbon-numbered mycolic acids, which often overlap each other on gas chromatograms, and the composition of three homologous mycolic acids with different alpha units (C22:0, C24:0, and C26:0) were clearly determined by mass chromatography monitoring [M - 15]+ ions and [B - 29]+ ions, respectively. The molecular species composition of alpha-mycolic acids and their average carbon numbers (av. cn.) as a simple expression of the composition were calculated from the mass chromatograms. Each mycobacterial species examined was demonstrated to possess a characteristic profile of alpha-mycolic acid composition...