Etudes sur le mécanisme de remodelage des nucléosomes par ...

tel-00413908, version 1 - 7 Sep 2009
concentration (2M NaCl), the octamer of histones forms spontaneously, in vitro (Eickbush
and Moudrianakis, 1978).
Besides histone fold, each histone has distinct N-terminal and C-terminal regions. N-terminal
tails of histones are located outside of nucleosomes and are subjected to covalent
modifications which may lead to modification of local chromatin structure either directly or
through other interacting proteins. These accessible regions serve as a platform for interaction
between chromatin and regulatory proteins. The amino-terminal parts of the histones do not
take part significantly in the structure of the nucleosome; they seem to be rather committed in
interactions with other proteins or others nucleosomes. Tails of the histones H2B and H4 in
particular are important for the formation of higher order structure of chromatin. The integrity
of the tail of H4 is necessary for the formation of 30 nm fiber (Dorigo et al., 2003) and the
amino-terminal part of H2B is necessary for the chromosome assembly (de la Barre et al.,
2000; de la Barre et al., 2001). This higher order architecture is facilitated and stabilized by
linker histones.
Figure I.3 Nucleosome assembly. The four core histones are organized in a tetramer (H3-H4)2 and
two dimers (H2A-H2B). Under ionic concentrations lower than 0.5 M and in the presence of DNA
these species are assembled to form the nucleosome or “nucleosomal core particle” (NCP). Adapted
from Richard Wheeler.
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