A DFT study of the reactivity indexes of ionic [4 + 2+] Diels-Alder cycloaddition to nitrilium and immonium ions

The global electrophilicity index, defined within the conceptual density functional theory (DFT), was used to classify the dienes and dienophiles currently used in Diels-Alder reactions on a unique scale of electrophilicity. The index, obtained within the Kohn-Sham scheme, is based on the HOMO and LUMO energies. A systematic study of the global reactivity indexes of the reagents involved in formal [4 + 2+] Diels-Alder cycloaddition reactions of nitrilium and immonium ions with isoprene is presente

Molecular characterization of XerS/difSL site-specific recombination system in Streptococcus suis

L'état circulaire du chromosome bactérien pose un problème particulier lors de la réplication. Un nombre impair d'événements de recombinaison homologue donne des chromosomes dimères concaténés qui ne peuvent pas être divisés en cellules filles. Pour résoudre ce problème, les bactéries ont mis au point un mécanisme de résolution des dimères basé sur un système de recombinaison spécifique au site. Ceci est effectué par le système Xer/dif. Dans ce système, les protéines Xer effectuent une réaction de recombinaison dans le site dif au niveau du septum cellulaire immédiatement avant la division cellulaire. Dans la plupart des bactéries, cette réaction est effectuée par deux recombinases, XerC et XerD. Cependant, Streptococcus suis, un agent pathogène zoonotique important utilise un système de recombinaison différent, constitué d'une seule enzyme recombinase appelée XerS, qui catalyse la réaction de recombinaison dans un site dif non conventionnel. Pour caractériser le mode de clivage de XerS, des expériences EMSA ont été réalisées en utilisant des fragments de PCR marqués par HEX et des "suicide substrates". Nos données suggèrent que 1.) XerS est capable de lier la séquence entière de difSL; 2.) XerS lie plus efficacement le côté gauche des mutants difSL incomplets que le côté droit; 3.) XerS coupe les brins supérieur et inférieur du site difSL, avec une réaction plus efficace au bas. 4.) Modifications des nucléotides de la région la plus externe ou de la région centrale changent les préférences de clivage. 5.) XerS n'a montré aucune activité spécifique sur un autre site dif non conventionnel des Firmicutes, 6.) XerS interagit avec la sous-unité FtsK-y. L'ensemble des résultats présentés permet de mieux comprendre le fonctionnement de la recombinaison XerS dans le système de recombinase unique de Streptococcus et comment cette recombinaison est régulée par des facteurs de l'hôte.The circular state of the bacterial chromosome presents a specific problem during replication. An odd number of homologous recombination events results in concatenated dimer chromosomes that cannot be partitioned into daughter cells. To solve this problem, bacteria have developed a mechanism of dimer resolution based on site-specific recombination system. This is performed by the Xer/dif system. In this system, the Xer proteins perform a recombination reaction in the dif site at the cell septum immediately prior to cell division. In most bacteria this reaction is performed by two recombinases, XerC and XerD. However, an important zoonotic pathogen; Streptococcus suis harbors a different recombination system, composed by a single recombinase enzyme called XerS, that catalyzes the recombination reaction in an unconventional dif site; difSL. A region characterized by two imperfect inverted repeat regions that flank a central region of 11 bp.To characterize the mode of cleavage of XerS, EMSA experiments were performed by using HEX-labelled PCR fragments and “nicked suicide substrates”. Our data suggests that; 1.) XerS is able to bind the entire difSL sequence; 2.) XerS binds more efficiently the left half side on incomplete difSL mutants than the right half side; 3.) XerS cleaves both the top and bottom strands of the difSL site, with a more efficient reaction at the bottom strand; 4.) Nucleotides at the outermost region of a T rich region seem to be determinant for binding selectivity and modifications of the extra spacing between the inverted repeat arms as well as length modifications of the central region change cleavage preference. 5.) XerS did not show any specific activity on another unconventional dif site in Firmicutes, as tested on difH. 6.) XerS interacts with FtsK-y subunit. This research aims to understand how XerS recombination works in the single recombinase system of Streptococcus and how this recombination is regulated by host factors. Exploration of these recombinases will provide a better understanding of the mechanisms of DNA exchange and genome stability in bacteria. It can also increase our knowledge of the evolution and speciation of recombinogenic bacteria

Epigenetic Mechanisms in Head and Neck Cancer

Head and neck cancer (HNC) is one of the most prevalent human malignancies, affecting different anatomic sites of the upper aerodigestive tract (UADT) such as the oral cavity, larynx, and naso-, oro-, and hypopharynx. HNC develops through the accumulation of multiple genetic and epigenetic alterations in a multistep process. In this issue, the aim is to describe epigenetic mechanisms behind HNC. The main mechanisms evaluated are DNA methylation, posttranslational histone modification, and noncoding RNAs

Antecedente macrosomía fetal como factor de riesgo para diabetes gestacional en el Hospital Belén de Trujillo

Demostrar que el antecedente de macrosomía fetal es factor de riesgo para diabetes gestacional en el Hospital Belén de Trujillo. Material y Métodos: Se llevó a cabo un estudio de tipo analítico, observacional, retrospectivo, de casos y controles. La población de estudio estuvo constituida por 106 gestantes primíparas; quienes se dividieron en 2 grupos: con y sin diabetes gestacional. Resultados: No se encontraron diferencias significativas entre los grupos de estudio en relacion a edad materna, edad gestacional y procedencia. La frecuencia de antecedente de macrosomia fetal en gestantes con diabetes fue 23%. La frecuencia de antecedente de macrosomia fetal en gestantes sin diabetes fue 7%. El antecedente de macrosomia fetal es factor de riesgo para diabetes gestacional con un odds ratio de 3.58 el cual fue significativo. Conclusiones: El antecedente de macrosomía fetal es factor de riesgo para diabetes gestacional en el Hospital Belén de Trujillo.Show that the history of fetal macrosomia is a risk factor for gestational diabetes in the Bethlehem Hospital of Trujillo. Material and Methods: An analytical study, observational, retrospective, casecontrol type is carried out. The study population consisted of 106 primiparous pregnant; who they were divided into 2 groups: with and without gestational diabetes. Results: No significant differences between groups study in relation to maternal age, gestational age and origin were found. The frequency of history of fetal macrosomia in pregnant women with diabetes was 23 %. The frequency of history of fetal macrosomia in pregnant women without diabetes was 7%. The history of fetal macrosomia is a risk factor for gestational diabetes with an odds ratio of 3.58 which was significant. Conclusions: The history of fetal macrosomia is a risk factor for gestational diabetes in the Bethlehem Hospital of Trujillo

Optimizing HARQ and relay strategies in limited feedback communication systems

One of the key challenges for future communication systems is to deal with fast changing channels due to the mobility of users. Having a robust protocol capable of handling transmission failures in unfavorable channel conditions is crucial, but the feedback capacity may be greatly limited due to strict latency requirements. This paper studies the hybrid automatic repeat request (HARQ) techniques involved in re-transmissions when decoding failures occur at the receiver and proposes a scheme that relies on codeword bundling and adaptive incremental redundancy (IR) to maximize the overall throughput in a limited feedback system. In addition to the traditional codeword extension IR bits, this paper introduces a new type of IR, bundle parity bits, obtained from an erasure code across all the codewords in a bundle. The type and number of IR bits to be sent as a response to a decoding failure is optimized through a Markov Decision Process. In addition to the single link analysis, the paper studies how the same techniques generalize to relay and multi-user broadcast systems. Simulation results show that the proposed schemes can provide a significant increase in throughput over traditional HARQ techniques