Aproveitamento do calor disponível nas râmolas da Tintojal

Bourgeois Léon. Arrêté fixant la date de l'ouverture du concours pour l'obtention des bourses de licence. In: Bulletin administratif de l'instruction publique. Tome 47 n°898, 1890. p. 367

The plant-specific DDR factor SOG1 increases chromatin mobility in response to DNA damage

Homologous recombination (HR) is a conservative DNA repair pathway in which intact homologous sequences are used as a template for repair. How the homology search happens in the crowded space of the cell nucleus is, however, still poorly understood. Here, we measure chromosome and double-strand break (DSB) site mobility in Arabidopsis thaliana, using lacO/LacI lines and two GFP-tagged HR reporters. We observe an increase in chromatin mobility upon the induction of DNA damage, specifically at the S/G2 phases of the cell cycle. This increase in mobility is lost in the sog1-1 mutant, a central transcription factor of the DNA damage response in plants. Also, DSB sites show particularly high mobility levels and their enhanced mobility requires the HR factor RAD54. Our data suggest that repair mechanisms promote chromatin mobility upon DNA damage, implying a role of this process in the early steps of the DNA damage response

Terrorism in the Political Landscape of Post-peace Accord in Colombia

En Colombia el terrorismo no es una amenaza nueva a la seguridad nacional. Históricamente el terrorismo ha estado estrechamente vinculado a la existencia del conflicto armado interno y a la evolución del método de acción de sus actores principales o periféricos (guerrilleros, narcotraficantes o paramilitares). El presente artículo tiene como objetivo analizar los tipos de terrorismo que han existido en Colombia, así como la manera en la que ha afectado la seguridad, para presentar la evolución del terrorismo en el contexto político nacional hasta el escenario actual del posacuerdoIn Colombia, terrorism is not a new threat to national security. Terrorism historically has been closely linked to the existence of an internal armed conflict and to the evolution of the “method of action” (método de acción) carried out by its main and secondary actors (guerrilla fighters, drug traffickers, militiamen). This article aims to analyze the different types of terrorism that have existed in Colombia as well as the way they have affected security and, finally, present its evolution in the national political context, from the signing of the most recent peace accord to the present

A bona fide La protein is required for embryogenesis in Arabidopsis thaliana

Searches in the Arabidopsis thaliana genome using the La motif as query revealed the presence of eight La or La-like proteins. Using structural and phylogenetic criteria, we identified two putative genuine La proteins (At32 and At79) and showed that both are expressed throughout plant development but at different levels and under different regulatory conditions. At32, but not At79, restores Saccharomyces cerevisiae La nuclear functions in non-coding RNAs biogenesis and is able to bind to plant 3′-UUU-OH RNAs. We conclude that these La nuclear functions are conserved in Arabidopsis and supported by At32, which we renamed as AtLa1. Consistently, AtLa1 is predominantly localized to the plant nucleoplasm and was also detected in the nucleolar cavity. The inactivation of AtLa1 in Arabidopsis leads to an embryonic-lethal phenotype with deficient embryos arrested at early globular stage of development. In addition, mutant embryonic cells display a nucleolar hypertrophy suggesting that AtLa1 is required for normal ribosome biogenesis. The identification of two distantly related proteins with all structural characteristics of genuine La proteins suggests that these factors evolved to a certain level of specialization in plants. This unprecedented situation provides a unique opportunity to dissect the very different aspects of this crucial cellular activity

Arabidopsis thaliana XRN2 is required for primary cleavage in the pre-ribosomal RNA

Three Rat1/Xrn2 homologues exist in Arabidopsis thaliana: nuclear AtXRN2 and AtXRN3, and cytoplasmic AtXRN4. The latter has a role in degrading 3′ products of miRNA-mediated mRNA cleavage, whereas all three proteins act as endogenous post-transcriptional gene silencing suppressors. Here we show that, similar to yeast nuclear Rat1, AtXRN2 has a role in ribosomal RNA processing. The lack of AtXRN2, however, does not result in defective formation of rRNA 5′-ends but inhibits endonucleolytic cleavage at the primary site P in the pre-rRNA resulting in the accumulation of the 35S* precursor. This does not lead to a decrease in mature rRNAs, as additional cleavages occur downstream of site P. Supplementing a P-site cleavage-deficient xrn2 plant extract with the recombinant protein restores processing activity, indicating direct participation of AtXRN2 in this process. Our data suggest that the 5′ external transcribed spacer is shortened by AtXRN2 prior to cleavage at site P and that this initial exonucleolytic trimming is required to expose site P for subsequent endonucleolytic processing by the U3 snoRNP complex. We also show that some rRNA precursors and excised spacer fragments that accumulate in the absence of AtXRN2 and AtXRN3 are polyadenylated, indicating that these nucleases contribute to polyadenylation-dependent nuclear RNA surveillance