Aislamiento y caracterizacion parcial de fracciones con actividad ribonucleasa a partir del latex de calotropis procera (Aiton) W.T. Aiton y pedilanthus tithymaloides (L.) poit / Isolation and partial characterization of fractions with ribonuclease activity from latex of calotropis procera (Aiton) W.T. Aiton and pedilanthus tithymaloides (L.) poit

Con el objetivo de aislar y caracterizar parcialmente las enzimas ribonucleasas (RNasas) contenidas en el látex de Calotropis procera y Pedilanthus tithymaloides, se colectaron muestras de plantas adultas. Las proteínas solubles fueron extraídas con acetato de sodio y centrifugación a 16.000 x g durante 15 min y fraccionadas por cromatografía de intercambio iónico. Se estimó la masa molecular a través de ecuaciones de regresión lineal. Se realizaron pruebas de glicosilación. En ambas especies, las proteínas con actividad RNasa presentaron una masa molecular entre 28 y 30 kDa. No existe evidencia de proteínas glicosiladas en el látex de C. procera. En P. tithymaloides la RNasa es una proteína glicosilada.

In order to isolate and characterize partially ribonucleases (RNases) enzymes contained in the latex from Calotropis procera and Pedilanthus tithymaloides, samples were collected from mature plants. Soluble proteins were extracted with sodium acetate and centrifugation at 16,000 xg for 15 min and fractionated by ion exchange chromatography. Molecular mass was estimated by linear regression equations. Glycosylation tests were conducted. In both species, proteins with RNase activity showed a molecular mass between 28 and 30 kDa. No evidence of glycosylated proteins in latex from C. procera. In P. tithymaloides, RNase may be a glycosylated protein.

Efecto de la insulina humana sobre el crecimiento y expresión de proteínas celulares de Klebsiella pneumoniae aislada de pie diabético / Effect of human insulin on growth and cellular protein expression of Klebsiella pneumoniae isolated from diabetic foot infections

Algunos microorganismos patógenos aumentan su proliferación al cultivarlos en presencia de insulina, por lo tanto, la hiperinsulinemia podría influir sobre las infecciones de pacientes diabéticos. En este trabajo se determinó el efecto de la insulina sobre el crecimiento y expresión de proteínas celulares de Klebsiella pneumoniae aislada de pie diabético. Las bacterias se cultivaron en medio Luria-Bertani en presencia o en ausencia de insulina humana. El crecimiento se determinó midiendo la DO600 de los cultivos hasta alcanzar la fase estacionaria; se colectaron bacterias a diferentes tiempos para extraer sus proteínas celulares (extractos) y analizarlas mediante electroforesis en geles de poliacrilamida-SDS y densitometría cuantitativa. En presencia de insulina (0,5 U/mL) el crecimiento bacteriano se incrementó en 40% respecto al control en las fases logarítmica temprana y media. Todos los perfiles electroforéticos de los extractos mostraron 27 bandas polipeptídicas (rango 150-9 kDa). La expresión del 41% de estas bandas aumentó en los extractos de las bacterias cultivadas con insulina, respecto a los controles, mientras que la expresión del 22% disminuyó. Los resultados indicaron que la insulina incrementó la proliferación y moduló la expresión genética de K. pneumoniae, sugiriendo que la hiperinsulinemia podría favorecer la severidad de infecciones en pacientes diabéticos.

Some pathogens increase their proliferation when cultured in the presence of insulin, therefore, hyperinsulinemia may influence diabetic infections. In this work we determine the effect of insulin on growth and cellular protein expression from Klebsiella pneumoniae isolated from diabetic foot infections. Bacteria were grown in Luria-Bertani medium in the presence and absence of human insulin. Growth was determined by measuring OD600 of the cultures until reached the stationary phase. In order to extract cellular proteins, bacteria were collected at different times to obtain extracts that were analyzed by electrophoresis on SDS-polyacrylamide gels and quantitative densitometry. In the presence of insulin (0.5 U/mL) bacterial growth increased by 40% compared with control in the early and middle logarithmic phase. All electrophoretic profiles of the extracts showed 27 polypeptide bands (range 150-9 kDa). The expression of 41% of these bands increased in extracts from bacteria grown with insulin when compared with controls, whereas protein expression decreased by 22%. The results indicated that insulin increased K. pneumoniae proliferation and modulated gene expression, suggesting that hyperinsulinemia could contribute to the severity of the infections in diabetic patients.

[5´cap -independent translation of dengue virus genomic RNA]. / Traducción independiente de la estructura 5´cap del ARN genómico del virus dengue.

OBJETIVES: To analyze the involvement of methyl guanosine triphosphate cap (5’cap) and the start site of the genomic RNA of Dengue virus serotype 2 (DENV-2) American genotype in translation, using a cell-free system prepared from human placenta. MATERIALS AND METHODS: The recombinant plasmid pTZ18R-D2 was prepared containing DNA encoding the 5’UTR and the first 201 nucleotides of the viral capsid. This plasmid was used to transcribe the corresponding RNA (RNA-D2) without the 5’ cap. The RNA-D2 was translated in a system consisting of the postmitochondrial fraction (S-30) from human placenta and the incorporation of [14C] aminoacids in the presence of RNA-D2 and in its absence (control) was evaluated. Seven antisense oligonucleotides (OAs1-7) directed against sequences of the SLA, SLB and CHP structures of RNA-D2 were designed and the effect thereof on RNA-D2 translation was analyzed. RESULTS: The RNA-D2 produced a significant increase (p<0.001) in the incorporation of [14C] amino acids, with 75% stimulation of translational activity compared to the control. Analysis of the translation products showed peak incorporation corresponding to peptides with apparent molecular weight close to the expected (7.746 kDa).The OAs5, complementary to a sequence of SLB structure of RNA-D2, completely inhibited translation. CONCLUSIONS: The RNA-D2 was translated specifically and efficiently under conditions similar to human intracellular conditions, by an alternative 5’ cap-independent mechanism, which would involve the SLB structure. This mechanism might be seen as an aim in the development of antisense therapies to inhibit virus replication.

Traducción independiente de la estructura 5´cap del ARN genómico del virus dengue / 5´cap-independent translation of dengue virus genomic RNA

Objetivos. Analizar la participación de la caperuza metil-guanosín-trifosfato (5´cap) y de la región inicial del ARN genómico del virus dengue serotipo 2 (DENV-2) genotipo Americano en la traducción, utilizando un sistema libre de células obtenido de placenta humana. Materiales y métodos. Se preparó el plásmido recombinante pTZ18R-D2 conteniendo el ADN que codifica la 5´UTR y los primeros 201 nucleótidos de la cápside viral. Este plásmido se utilizó para transcribir el ARN correspondiente (ARN-D2), sin la 5´cap. El ARN-D2 fue traducido en un sistema constituido por la fracción posmitocondrial (S-30) de placenta humana y se evaluó la incorporación de [14C] aminoácidos en presencia del ARN-D2 y en su ausencia (control). Se diseñaron siete oligonucleótidos antisentido (OAs1-7) dirigidos contra secuencias de las estructuras SLA, SLB y cHP del ARN-D2 y se analizó el efecto de los mismos sobre la traducción ARN-D2. Resultados.El ARN-D2 produjo un incremento significativo (p<0,001) en la incorporación de [14C] aminoácidos, con estimulación del 75% de la actividad traduccional respecto al control. El análisis de los productos de traducción mostró un pico de incorporación correspondiente a péptidos con peso molecular aparente cercano al esperado (7,746 kDa). El OAs5, complementario a una secuencia de la estructura SLB del ARN-D2, inhibió completamente la traducción. Conclusiones. El ARN-D2 fue traducido de manera específica y eficiente, bajo condiciones semejantes a las intracelulares en humanos, por un mecanismo alternativo independiente de la 5´cap, que involucraría a la estructura SLB. Este mecanismo podría considerarse como blanco en el desarrollo de terapias antisentido para inhibir la reproducción del virus.

Objetives. To analyze the involvement of methyl guanosine triphosphate cap (5Æcap) and the start site of the genomic RNA of Dengue virus serotype 2 (DENV-2) American genotype in translation, using a cell-free system prepared from human placenta. Materials and methods. The recombinant plasmid pTZ18R-D2 was prepared containing DNA encoding the 5ÆUTR and the first 201 nucleotides of the viral capsid. This plasmid was used to transcribe the corresponding RNA (RNA-D2) without the 5Æ cap. The RNA-D2 was translated in a system consisting of the postmitochondrial fraction (S-30) from human placenta and the incorporation of [14C] aminoacids in the presence of RNA-D2 and in its absence (control) was evaluated. Seven antisenseoligonucleotides (OAs1-7) directed against sequences of the SLA, SLB and CHP structures of RNA-D2 were designed and the effect thereof on RNA-D2 translation was analyzed. Results.The RNA-D2 produced a significant increase (p<0.001) in the incorporation of [14C] amino acids, with 75% stimulation of translational activity compared to the control. Analysis of the translation products showed peak incorporation corresponding to peptides with apparent molecular weight close to the expected (7.746 kDa).The OAs5, complementary to a sequence of SLB structure of RNA-D2, completely inhibited translation. Conclusions. The RNA-D2 was translated specifically and efficiently under conditions similar to human intracellular conditions, by an alternative 5Æ cap-independent mechanism, which would involve the SLB structure. This mechanism might be seen as an aim in the development of antisense therapies to inhibit virus replication.

Citotoxicidad in vitro de extractos laticiferos de Calotropis procera (Aiton) W.T. Aiton y Pedilanthus tithymaloides (L.) Poit / In vitro cytotoxicity of laticifers extracts from Calotropis procera (Aiton) WT and Pedilanthus tithymaloides (L) Poit

In order to assess the anticancer action of extracts obtained by latex from Calotropis procera and Pedilanthus tithymaloides, samples were collected from adult plants. Soluble proteins were extracted with 16 uL of 50 mM sodium acetate pH 5/ug integral latex and centrifugation at 16,000 x g for 15 min, the supernatant was named "latex crude extract" (LCE). The "latex methanolic extract" (LME) was obtained on dried latex. Both extracts were tested in vitro by cytotoxic and cytostatic activity in Jurkat cell cultures. Cellular viability, proliferation, necrosis and apoptosis were evaluated. LCE and LME of C. procera were found with cytotoxic and cytostatic activity after 24 incubation hours (p < 0,05) with doses from 1ug/mL. The LCE and LME of P. tithymaloides presented cytotoxic effect (p < 0,05) from 50 ug/mL and from 1ug/mL, respectively.

Con el objetivo de evaluar el potencial anticanceroso de extractos de látex de Calotropis procera y Pedilanthus tithymaloides se colectaron muestras de plantas adultas. Las proteínas solubles fueron extraídas con 16 uL de acetato de sodio 50 mM pH 5/ug de látex integral y centrifugación a 16.000 x g durante 15 min, denominándose al sobrenadante “extracto crudo de látex” (ECL). El “extracto metanólico de látex” (EML) se obtuvo sobre látex deshidratado. Ambos extractos fueron probados en su actividad citotóxica y citostática in vitro sobre cultivos de células Jurkat. Se realizaron estudios de viabilidad, proliferación, necrosis y apoptosis celular. El ECL y el EML de C. procera presentaron actividad citotóxica y citostática después de 24 y 48 horas de incubación (p < 0,05) con dosis desde 1 ug/mL. Los ECL y EML de P. tithymaloides presentaron efectos citotóxicos (p < 0,05) a partir de 50 ug/mL y desde 1 ug/mL respectivamente.

Efecto de la insulina en Saccharomyces cerevisiae: estimulación de la actividad enzimática de piruvato quinasa, expresión de proteínas citoplasmáticas y proliferación celular / Insulin effect in Saccharomyces cerevisiae: stimulation of pyruvate kinase activity, citoplasmatic proteins expression and cell proliferation

La levadura Saccharomyces cerevisiae es sensible a la insulina de mamíferos y actúa en el metabolismo de carbohidratos. Sin embargo, no hay estudios de su efecto en las enzimas glucolíticas de este microorganismo. Este trabajo demuestra que la insulina estimula la actividad de piruvato quinasa en S. cerevisiae durante su crecimiento en medio rico suplementado con glucosa y en condiciones aeróbicas. En la fase logarítmica temprana, la máxima estimulación sobre el control se observó en presencia de 3 µM de insulina (actividad específica: 701 U/mg proteína, 404% de estimulación; actividad absoluta: 1,73 U/10(6) células, 652% de estimulación), sugiriendo un efecto sobre la regulación de la expresión genética de la enzima. La presencia de 1,2-3 µM de la hormona estimuló en 51-68% la expresión de las proteínas citoplasmáticas y, a concentraciones mayores (4,5-9 µM), también estimuló en 25-32% la proliferación celular, indicando hiperplasia e hipertrofia celular de acuerdo a la concentración de la insulina en el medio. El efecto de la hormona disminuyó en la fase logarítmica tardía de crecimiento, sugiriendo un periodo de acción, posiblemente por un mecanismo regulatorio dependiente de nutrientes. Este sistema puede servir como modelo para estudiar muchos de los efectos moleculares de la insulina no conocidos aún.

Saccharomyces cerevisiae yeast is sensitive to mammal’s insulin and acts in carbohydrate metabolism. Nevertheless, there are no studies of its effects on the glycolytic enzymes of this microorganism. This study shows that insulin stimulates pyruvate kinase activity in S. cerevisae during its growth in rich glucose supplemented media, and under aerobic conditions. In the early logarithmic phase, the maximum stimulation over control was seen in presence of 3 µM insulin (specific activity: 701 U/mg protein, 404% stimulation; absolute activity: 1.73 U/10(6) cells, 652% stimulation), suggesting an effect over the regulation of the genetic expression of the enzyme. The presence of 1.2-3 µM of insulin stimulated the expression of cytoplasmic proteins in 51-68% and at higher concentrations (4.5-9 µM) it also stimulated cell proliferation in 25-32%, indicating cell hyperplasia and hypertrophy according to the hormone concentration in the medium. The effect of the insulin decreased in the late logarithmic growth phase, suggesting a period of action, possibly due to a nutrient dependent regulatory mechanism. This system can serve as model to study many of the molecular effects of insulin not yet known.

Cultivation and molecular identification of Ehrlichia canis and Ehrlichia chaffeensis from a naturally co-infected dog in Venezuela.

BACKGROUND: Diagnosis of canine ehrlichiosis in Venezuela is normally performed by examination of buffy coat smears (BCS). Characteristic inclusion bodies are frequently observed in leukocytes and platelets from dogs with clinical signs of the disease. OBJECTIVE: The purpose of this study was to investigate the co-infection of a dog with Ehrlichia canis and E hrlichia chaffeensis using microbiological and molecular techniques. METHODS: Primary cultures of monocytes from a dog showing signs of ehrlichiosis were performed. Ehrlichial inclusions in blood cells were demonstrated by BCS and in cultured cell smears with direct immunofluorescence and Dip Quick staining. Nested PCR analysis was performed with DNA from blood samples and cultures, using primers specific for E. canis and E. chaffeensis. The amplified DNA fragments were sequenced to confirm the specificity of the amplifications. RESULTS: The BCS of the naturally infected dog contained intracellular morulae. Ehrlichial inclusions were observed 9 days after inoculation of the primary cultures. After 3 passages with monocytes from a healthy dog, 65% of infected cells, and cells with >60 morulae were observed. A healthy female German Shepherd dog, seronegative for E. canis and E. chaffeensis antigens and without contact to ticks, was inoculated with an infected culture. The animal developed signs of canine monocytic ehrlichiosis and became seropositive. Nested PCR results and sequencing of amplified DNA fragments demonstrated the simultaneous presence of E. canis and E. chaffeensis in both dogs. CONCLUSIONS: This is the first report of E. chaffeensis in dogs in South America. This organism was previously identified in dogs by PCR only in the United States.

Shine-Dalgarno interaction prevents incorporation of noncognate amino acids at the codon following the AUG.

During translation, usually only one in approximately 400 misincorporations affects the function of a nascent protein, because only chemically similar near-cognate amino acids are misincorporated in place of the cognate one. The deleterious misincorporation of a chemically dissimilar noncognate amino acid during the selection process is precluded by the presence of a tRNA at the ribosomal E-site. However, the selection of first aminoacyl-tRNA, directly after initiation, occurs without an occupied E-site, i.e., when only the P-site is filled with the initiator tRNA and thus should be highly error-prone. Here, we show how bacterial ribosomes have solved this accuracy problem: In the absence of a Shine-Dalgarno (SD) sequence, the first decoding step at the A-site after initiation is extremely error-prone, even resulting in the significant incorporation of noncognate amino acids. In contrast, when a SD sequence is present, the incorporation of noncognate amino acids is not observed. This is precisely the effect that the presence of a cognate tRNA at the E-site has during the elongation phase. These findings suggest that during the initiation phase, the SD interaction functionally compensates for the lack of codon-anticodon interaction at the E-site by reducing the misincorporation of near-cognate amino acids and prevents noncognate misincorporation.

Extracción y purificación de glucosa oxidasa para fines diagnósticos producida en medios a base de fertilizantes y azúcar industrial / Extraction and purification of glucose oxidase for diagnostic purposes produced in media based on fertilizers and industrial sugar

La enzima glucosa oxidasa (GOX) es componente esencial de reactivos para determinación de glicemia y otros parámetros paraclínicos. Para su producción suele utilizarse Aspergillus niger cultivado en medios con sustratos costosos de grado analítico. Por tanto, se planteó purificar GOX producida por A. niger, cultivado con nutrientes complejos y económicos, y evaluar su efectividad en mediciones de concentración de glucosa. Para ello se formularon 4 tipos de medio, uno estándar y tres alternativos con azúcar industrial y fertilizantes. Los cultivos se realizaron en fiolas con 50 mL de medio bajo un diseño de bloques al azar, evaluando el crecimiento y la actividad enzimática. El medio alternativo con mejor rendimiento fue seleccionado para producción en biorreactores de 5 L y posterior purificación de GOX (fraccionamiento salino y cromatografías en Sephadex G-25 y DEAE-Sephacel). Se obtuvieron altos rendimientos de enzima (7 mg por carga) de alta pureza (39000 U/g) y un K M aparente para glucosa de 22 ± 1 mM. El reactivo de diagnóstico formulado presentó un intervalo de linealidad óptima (de 50 a 600 mg/dL de glucosa). Por lo que se concluyó que los sustratos en el medio de cultivo alternativo no interfieren en la calidad y cantidad del producto purificado.

The enzyme glucose oxidase (GOX) is an essential component of reagents used for determining blood sugar and other clinical parameters. Aspergillus niger grown in media prepared with expensive analytical grade substrates is used for its production. Therefore, we decided to purify GOX produced by A. niger grown in media with complex and inexpensive nutrients and to evaluate its efficiency in glucose concentration measurement assays. For this purpose we formulated four types of media, one standard and other three alternatives in which we used industrial sugar and fertilizers. The cultures were done in 50 mL flasks under a random block design, evaluating growth and enzymatic activity. The alternative medium with the best yield was selected for production in 5 liter bioreactors and later GOX purification (saline fractioning and Sephadex G-25 and DEAE-Sephacel chromatography ). Two large enzyme yields were obtained (7 mg per load), highly purified (39000 U/g), and with an apparent 22 ± 1 mM glucose K M. The diagnostic reagent formulated presented an optimal linearity interval (between 50 and 60 mg/dL glucose). Therefore, it was concluded that the substrates in the alternative culture medium did not interfere in the quality and quantity of the purified product.

Prior interaction of ATP with yeast mRNAs enhances protein synthesis at the initiation step.

ATP hydrolysis is important for different stages of the protein synthesis process. A novel effect of this nucleotide was detected using mRNAs isolated from S. cerevisiae after phenol extraction of polysomes. When polysomal mRNA (pmRNA) or poly(A)(+) RNA were preincubated with ATP (approximately 3 mM, near physiological concentration), their translational activity in a cell-free system from yeast was stimulated 2-3 fold. This increased translational activity is specific for the poly(A)(+) RNA fraction, correlates with facilitated assembly of 80S initiation complexes, and is associated to increased synthesis of high molecular weight polypeptides. TCA precipitation assays of RNA incubated with [(14)C]ATP suggested an association of the nucleotide with the nucleic acid. The amount of [(14)C]ATP co-precipitated was dependent on magnesium (optimum at 5-6 mM), was partially inhibited by monovalent ions, and was maximal with poli(A)(+) RNA. Existence of RNA-associated kinases or ATPases appear unlikely since neither phosphorylation nor nucleotide hydrolysis were observed during preincubation of pmRNA with ATP. Another evidence of ATP-RNA interaction was an increased absorbance at 260 nm after incubation suggesting unwinding of the RNA secondary structure. Therefore, preincubation with ATP may affect the conformation of mRNAs and thereby facilitate the initiation of protein synthesis. This event could be part of an in vivo energy-dependent mechanism for translational control.

Actividad ATP hidrolasa asociada a ribosomas humanos como nuevo indicador para evaluar fármacos in vitro / Human ribosome-associated ATPase activiry as a new indicator for in vitro evaluation of drugs

En todos los ribosomas de mamíferos estudiados hasta el presente se ha identificado una actividad ATP hidrolasa (ATPasa) asociada. Su papel en el mecanismo de síntesis de proteínas está siendo estudiado actualmente y existen evidencias de homología funcional con el factor de elongación 3 (EF3) de hongos. Para caracterizar la actividad ATPasa ribosomal humana, se aislaron ribosomas 80S de placenta humana y se estudiaron los parámetros cinéticos de dicha actividad. La velocidad de hidrólisis (0,50 ± 0,05 nmol Pi/A260 80S/min) a concentración fisiológica de ATP (3 mmol/L) y la constante de catálisis aparente (0,5 ± 0,1 sˉ¹) están en el rango de Vmax (0,65 nmol Pi/A260 80S/min) y Km (58 µmol/L), determinados por análisis de Lineweaver-Burk, también son comparables a los reportados para ribosomas de otros mamíferos. El análisis de Eadie-Hofstee indicó la presencia de cooperativa positiva, con un Km aparente de 15 µmol/L para la forma más activa de la enzima. La ATPasa fue inhibida por metavanadato (inhibidor de EF3), y por los antibióticos emetina (inhibidor de la translocación) y anisomicina (actúa sobre los sitios ribosomales A y E). Además, la actividad no fue afectada por antibióticos específicos para otras funciones ribosomales en eucariotes ni tampoco por bloqueadores del ribosoma bacteriano. La sencillez y bajo costo del ensayo de actividad ATPasa ribosomal lo hacen ideal para el diseño de pruebas de alto rendimiento in vitro que harían posible tomar decisiones tempranas sobre el posible uso terapéutico en humanos de nuevos antibióticos o funguicidas

Optimización de un sistema de traducción in vitro derivado de placenta humana para la evaluación de antibióticos / An in vitro translation system derived from human placenta for evaluation of antibiotics

Un sistema de traducción in vitro derivado de placenta humana es una herramienta útil para estimar el efecto que tendrían antibióticos nuevos sobre la síntesis de proteínas en células humanas. Una modalidad simple de ensayo in Vitro es la síntesis de polifenilalanina o poli(Phe), dependiente del ARN sistético poli(U). Para optimizar este ensayo, se purificó ARNtPhe homólogo, partiendo de ARNt total de placenta, mediante una combinación de cromatografía hidrofóbica y de alta presión en fase reversa (RP-HPLC). Al incorporar el ARNTPhe purificado a los ensayos se duplicó la eficiencia de síntesis de polo(Phe) con respecto a la obtenida con un ARNt total heterólogo de levadura. El sistema de ensayo optimizado fue usado para determinar el efecto de antibióticos sobre la elongación de polipéptidos por ribosomas humanos. La actividad ribosomal eucariota (ciclo-heximida y emetina, IC50 ˜= 40-60 µmol/L y 10-30 µmol/L, respectivamente). Por el contrario, antibióticos que actúan sobre el ribosoma bacteriano (cloranfenicol, azitromicina, y clindamicina) no mostraron efecto inhibitorio aún a concentraciones altas (hasta 1 mmol/L). Estos resultados demuestran la sensibilidad diferencial esperada del sistema in vitro y su potencialidad para ser utilizado en una evaluación temprana y rápida del efecto de antibióticos de nueva generación sobre la síntesis de proteínas con ribosomas humanos. Por lo tanto, el sistema de ensayo in Vitro permitiría seleccionar aquellos compuestos con mejores posibilidades para las pruebas posteriores necesarias para establecer su uso terapéutico en humanos

Maintaining the ribosomal reading frame: the influence of the E site during translational regulation of release factor 2.

Maintenance of the translation reading frame is one of the most remarkable achievements of the ribosome while decoding the information of an mRNA. Loss of the reading frame through spontaneous frameshifting occurs with a frequency of one in 30,000 amino acid incorporations. However, at many recoding sites, the mechanism that controls reading frame maintenance is switched off. One such example is the programmed +1 frameshift site of the prfB gene encoding the termination factor RF2, in which slippage into the forward frame by one nucleotide can attain an efficiency of approximately 100%, namely, four orders of magnitude higher than normally observed. Here, using the RF2 frameshift window, we demonstrate that premature release of the E site tRNA from the ribosome is coupled with high-level frameshifting. Consistently, in a minimal system, the presence of the E site tRNA prevents the +1 frameshift event, illustrating the importance of the E site for reading-frame maintenance.

Efficient and faithful in vitro translation of natural and synthetic mRNA with human ribosomes.

Efficient systems for in vitro translation are of importance for biochemical and gene expression studies as well as for biotechnological developments. We optimized a cell-free translation system using subcellular fractions from human placenta and high quality placental tRNAs isolated using a simple and fast procedure. The postmitochondrial fraction or a reconstituted system containing soluble proteins plus polysomes were able to efficiently translate endogenous and exogenous mRNAs. Optima for ions, enzymes, tRNA and energy mix components were determined for a poly(U)-directed poly(Phe) synthesis test. The use of homologous tRNAPhe, omission of commercial creatine kinase, and addition of 3.5 mM spermidine at near physiological magnesium concentration (2.5 mM), were the most significant improvements. Under optimal conditions, poly(Phe) synthesis proceeded at a maximal initial rate of 1.2 Phe/80S/min at 37 degrees C, while natural mRNA translation by S-30 started at a near in vivo estimated rate of 0.3-0.5 amino acid/80S/sec. Furthermore, natural mRNA directed the synthesis of a family of polypeptides closely resembling the pattern of cytoplasmic proteins in both, molecular weight and relative amounts. This efficient and faithful system is of interest for biochemical studies of the human translational machinery, as well as a basis for screening new drugs affecting protein synthesis in pathogenic microorganisms.

Tripanosomiasis americana cerebral en un paciente con síndrome de inmunodeficiencia adquirida, diagnóstico por exámen directo y confirmado por reacción de polimerasa en cadena (PCR) en líquido cefalorraquídeo / A case report of a cerebral american trypanosomiasis in a patient with aids, diagnosed by direct examination of cerebrospinal fluid and confimred by pcr

Se describe la aparición de un cuadro meningoencefálico en un paciente con enfermedad de chagas 7 años después de que las pruebas para el virus de inmunodeficiencia adquirida (VIH) dieran positivas. Formas compatibles con tripomastigotes de Trypanosoma cruzi fueron visualizadas al microscopio de luz en LCR y posteriormente comprobadas como tales por reacción de polimerasa en cadena (PCR). El paciente fue tratado con benznidazol y ha sobrevivido 2 años al cuadro meningoencefálico con buena recuperación de las funciones cerebrales. Se trata del primer caso reportado en Venezuela donde la inmunosupresión, inducida por VIH, determinó una reactivación de la enfermedad de Chagas que involucró al SNC. La enfermedad de Chagas es endémica en Venezuela y en buena parte de Latinoamérica y es creciente el número de pacientes con VIH/SIDA, por lo que la probabilidad de coinfección debe ser tomada en cuenta a fin de iniciar un tratamiento antiparasitario oportuno. Se discute la importancia del examen del LCR para la detección de T. cruzi como patógeno oportunista en los cuadros meningoencefálicos de pacientes con VIH/SIDA, el uso del PCR como indicador temprano de la presencia de parásitos en sangre o tejidos y la posibilidad de iniciar tratamientos parasiticidas en todos los pacientes seropositivos para ambas enfermedades