Seminários

Colóquios do IF-UFF

Na próxima quarta-feira (27/03), às 15:45 h, na sala 201 do instituto de física, teremos um colóquio ministrado pelo Prof. Dr. Avinoam Ben-Shaul do Department of Physical Chemistry and the Fritz Haber Research Center (The Hebrew University of Jerusalem).

Título: DNA and RNA In and Out of Viral Capsids

Resumo: The genomic material of bacterial virus (bacteriophages) is double stranded (ds) DNA, and that of animal and plant viruses is generally single stranded (ss)RNA. The dsDNA in the protein capsid of the phage is extremely densely packed, and drastically bent, resulting in internal pressures reaching ~50 atmospheres. The work of packaging is provided by a motor protein producing forces of up to about 100pN. We shall mention some of the relevant (single molecule and other) experiments, outline the theories proposed to explain these experiments, and resolve the puzzling question why some theoretical approaches attribute the packaging free energy to entropic contributions while others to repulsive DNA-DNA interactions. RNA in animal and plant viruses is less densely packed. Its packaging within the viral capsid is a cooperative assembly-assembly process of the RNA and the capsid proteins. Due to partial matching of its bases, ssRNA folds on itself into branched structures composed of short double stranded duplexes connected by flexible loops. It will be shown that the sizes of viral RNAs, as measured by their radius of gyration or the ?maximum ladder distance? are smaller than those of non-viral RNA of the same length. We shall describe a simple model of RNA folding and some basic statistical properties of this ?branched polymer?. Treating the RNA as a branched polymer we shall show that its radius does not scale with chain length like ideal branched polymers but rather according to Rg~N1/3. We shall also explain the physical proximity of its 3' and 5' ends in most ssRNA structures. Finally, we shall describe some recent experimental results on viral assembly from the work of colleagues at UCLA, and try to interpret them theoretically. The work on these topics was done in close collaboration with the group of Bill Gelbart, UCLA.