[Todos] Primer Seminario INQUIMAE / DQIAQF -Lunes 4 de marzo 14hs

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Seminarios DQIAQF - INQUIMAE, Lunes 4 de marzo - 14 hs.

Aula de Seminarios INQUIMAE - DQIAQF
Facultad de Ciencias Exactas y Naturales
Ciudad Universitaria - Pab. 2  -  Piso 3

Physics of DNA and RNA in and out of viral capsids

A. Ben-Shaul,

Department of Physical Chemistry and  the Fritz Haber Research Center ,
The Hebrew University , Jerusalem 91904.

            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.