HCV IRES manipulates the ribosome to promote the switch from translation initiation to elongation.

The internal ribosome entry site (IRES) of the hepatitis C virus (HCV) drives noncanonical initiation of protein synthesis necessary for viral replication. Functional studies of the HCV IRES have focused on 80S ribosome formation but have not explored its role after the 80S ribosome is poised at the start codon. Here, we report that mutations of an IRES domain that docks in the 40S subunit's decoding groove cause only a local perturbation in IRES structure and result in conformational changes in the IRES-rabbit 40S subunit complex. Functionally, the mutations decrease IRES activity by inhibiting the first ribosomal translocation event, and modeling results suggest that this effect occurs through an interaction with a single ribosomal protein. The ability of the HCV IRES to manipulate the ribosome provides insight into how the ribosome's structure and function can be altered by bound RNAs, including those derived from cellular invaders

Evaluación de la frecuencia cardíaca y su relación con el remodelado ventricular en respuesta al ejercicio dinámico como indicador de función autonómica en atletas, pesistas y maratonistas

This study was performed to evaluate 118 subjects (athlete’s runners, weight lifters, with control group of healthy subjects sedentary) who have performed stress with treadmill test to evaluate the vagal reserve, as the grade of acceleration of the heart rate (HR) after the 10 second of starting the exercise and the Δ1 and Δ2 respectively,. Transtoracic echocardiography was performed to evaluate diameters and ventricular volumes and diastolic function to determine the patterns of ventricular filling. The sample was divided into three groups: Group I Sedentary, Group II Runners, and the Group III Weight Lifters. Group II was those with vagal predominance in the test with a Δ1 de m=36±14 lat/min and Δ2 de m=58±15 lat/min (p0.0001 and expressed left ventricular (LV) geometric patterns given by higher LV diameter and higher volumes indexed (m= 63±82 mm) p 0.0001 in relation to the group I and III. On the other hand, the weight lifters expressed the less HR recovery after the exercise and the higher wall thickness and higher relation E/e (m=8±3). p0.0001. This study allows us to affirm on the vagal predominance and less stiffness, was observed in endurance athletes, compared to athlete’s static and also allows opening a light to the explanation of the possible reasons to elucidate this phenomenon.Se estudiaron 113 sujetos (atletas maratonistas, atletas pesistas y controles sedentarios sanos) a los que se les realizó una prueba de esfuerzo en banda sin fin, para evaluar la reserva vagal, definida por la aceleración de la frecuencia cardiaca (FC) a los 10 segundos de iniciado el ejercicio, como la recuperación de la FC al primer minuto y el segundo minuto después de la realización del ejercicio dinámico, Δ1 y Δ2 respectivamente. Se realizó ecocardiograma transtoraxico para evaluar los índices de volúmenes ventriculares y la función diastólica, para determinar los patrones de llenado ventricular. La muestra se dividió en tres grupos: Grupo I: Control de Sedentarios Sanos, Grupo II: Maratonistas, Grupo III: Pesistas. Se observó que el Grupo II mostro mayor recuperación de la FC con un Δ1 de m=36±14 lat/min y Δ2 de m=58±15 lat/min, con mayor predominio vagal; asociado con un patrón geométrico ventricular izquierdo (VI) de mayores volúmenes indexados del VI de m= 63±82 mm con una p 0,0001 con relación a los del Grupo I y Grupo III. El Grupo III mostró menor recuperación de la FC con respecto a los demás grupos y mayor índice de la relación E/e’ (m=8±3), p 0,0001. Por lo tanto, este estudio nos permite concluir que los atletas mostraron un tono vagal aumentado y una menor rigidez VI con respecto a atletas estáticos y plantea los posibles mecanismos que explican este fenómeno

eIF2-dependent and eIF2-independent modes of initiation on the CSFV IRES: a common role of domain II

Specific interactions of the classical swine fever virus internal ribosomal entry site (IRES) with 40S ribosomal subunits and eukaryotic translation initiation factor (eIF)3 enable 43S preinitiation complexes containing eIF3 and eIF2–GTP–Met-tRNAMeti to bind directly to the initiation codon, yielding 48S initiation complexes. We report that eIF5B or eIF5B/eIF3 also promote Met-tRNAMeti binding to IRES–40S complexes, forming 48S complexes that can assemble elongation-competent ribosomes. Although 48S complexes assembled both by eIF2/eIF3- and eIF5B/eIF3-mediated Met-tRNAMeti recruitment were destabilized by eIF1, dissociation of 48S complexes formed with eIF2 could be out-competed by efficient subunit joining. Deletion of IRES domain II, which is responsible for conformational changes induced in 40S subunits by IRES binding, eliminated the sensitivity of 48S complexes assembled by eIF2/eIF3- and eIF5B/eIF3-mediated mechanisms to eIF1-induced destabilization. However, 48S complexes formed by the eIF5B/eIF3-mediated mechanism on the truncated IRES could not undergo efficient subunit joining, as reported previously for analogous complexes assembled with eIF2, indicating that domain II is essential for general conformational changes in 48S complexes, irrespective of how they were assembled, that are required for eIF5-induced hydrolysis of eIF2-bound GTP and/or subunit joining

HCV and CSFV IRES domain II mediate eIF2 release during 80S ribosome assembly

Internal ribosome entry site (IRES) RNAs from the hepatitis C virus (HCV) and classical swine fever virus (CSFV) coordinate cap-independent assembly of eukaryotic 48S initiation complexes, consisting of the 40S ribosomal subunit, eukaryotic initiation factor (eIF) 3 and the eIF2/GTP/Met-tRNA(i)(Met) ternary complex. Here, we report that these IRESes also play a functional role during 80S ribosome assembly downstream of 48S complex formation, in promoting eIF5-induced GTP hydrolysis and eIF2/GDP release from the initiation complex. We show that this function is encoded in their independently folded IRES domain II and that it depends both on its characteristic bent conformation and two conserved RNA motifs, an apical hairpin loop and a loop E. Our data suggest a general mode of subunit joining in HCV and HCV-like IRESes