Significance of Knotted Structures for Function of Proteins and Nucleic Acids
Poster Session I
5 – POS
Board 5
Topology of Eukaryotic Chromatin
Dominika Borek
, Zbyszek Otwinowski.
UT Southwestern Medical Center, Dallas, TX, USA.
How nucleosomes are arranged into higher-order structures in vivo is not understood, even
though the efficiency, precision, and microscopic images of metaphase chromosomes imply a
high level of structural organization. The current views of higher-order eukaryotic chromatin
organization involve either nucleosomal particles self-organizing by association and in a
hierarchical manner into higher-order structures or postulate the presence of polymer-melt with
ill-defined properties. Neither model agrees with the observed mechanical properties of
chromatin, nor with microscopic in situ and in vitro observations of chromatin in its native state,
nor with the distributive character of chromatids’ individualization.
We have re-analyzed published observations and experimental data from the last 50 years of
work on eukaryotic chromatin, looking for consistency with expanded biological knowledge. We
propose a new model of eukaryotic chromatin organization, where the higher-order structure of
chromatin is organized not only by proteins but also by DNA-based topological restraints that are
formed in kinetically controlled processes. Modifications of nucleosomal particles play an
important role in this model, serving as memory markers for remodeling complexes. The
proposed organization of eukaryotic chromatin agrees well with experimental data and explains
the specificity of distant cis-acting elements in transcription.
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