In polycistronic Qβ RNA, single-strandedness at one ribosome binding site directly affects translational initiations at a distal upstream cistron

In Qβ RNA, sequestering the coat gene ribosome binding site in a putatively strong hairpin stem structure eliminated synthesis of coat protein and activated protein synthesis from the much weaker maturation gene initiation site, located 1300 nucleotides upstream. As the stability of a hairpin stem comprising the coat gene Shine–Dalgarno site was incrementally increased, there was a corresponding increase in translation of maturation protein. The effect of the downstream coat gene ribosome binding sequence on maturation gene expression appeared to have occurred only in cis and did not require an AUG start codon or initiation of coat protein synthesis. In all cases, no structural reorganization was predicted to occur within Qβ RNA. Our results suggest that protein synthesis from a relatively weak translational initiation site is greatly influenced by the presence or absence of a stronger ribosome binding site located elsewhere on the same RNA molecule. The data are consistent with a mechanism in which multiple ribosome binding sites compete in cis for translational initiations as a means of regulating protein synthesis on a polycistronic messenger RNA

Caracterización de agregados pétreos de las Sierras Septentrionales de la provincia de Buenos Aires

En este estudio se realizaron diferentes ensayos físicos en triturados pétreos de canteras ubicadas en las Sierras Septentrionales de la provincia de Buenos Aires. A fin de efectuar una evaluación integral del desempeño de esos agregados para su uso en hormigón, se compararon los resultados de los ensayos físicos con estudios petrográficos previos (IRAM 1649). Se evaluaron siete canteras ubicadas en cercanías a las ciudades de Olavarría, Azul y Balcarce. Se realizaron análisis de densidad a granel y espacios vacíos (IRAM 1548), densidad relativa real, aparente y absorción de agua (IRAM 1533), granulometría (IRAM 1505) y se determinó la resistencia a la fragmentación (IRAM 1532). Los agregados presentan en general buenas características físicas, sin embargo, es indispensable efectuar comparaciones con el análisis petrográfico del material, ya que un buendesempeño en determinadas propiedades físicas puede no significar un buen comportamiento frente a la reacción álcali-sílice.In this study different physical characterization tests were performed in aggregates from quarries located in the Sierras Septentrionales of the province of Buenos Aires. In order to carry out a comprehensive evaluation of the performance of those aggregates for use in concrete, results of physical tests were compared with previous petrographic studies (IRAM 1649). Seven quarries located near Olavarría, Azul and Balcarce cities were evaluated. Bulk density and voids (IRAM 1548), relative real and apparent density, water absorption (IRAM 1533), granulometry (IRAM 1505) and fragmentation resistance (IRAM 1532) were determined. The aggregates generally present good physical characteristics; however, it is essential to compare with the petrographic analysis of the material, since a good performance in certain physical properties may not mean a good behaviour against alkali-silica reaction.Fil: Pérez Marfil, P.. Comision de Investigaciones Cientificas de la Provincia de Buenos Aires. Centro de Geologia Aplicada, Agua y Medio Ambiente.; ArgentinaFil: Priano, C.. Universidad Nacional del Sur. Departamento de Ingeniería; ArgentinaFil: Locati, Francisco. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Marfil, S.. Comision de Investigaciones Cientificas de la Provincia de Buenos Aires. Centro de Geologia Aplicada, Agua y Medio Ambiente.; Argentin