Article: The Nucleosome Untangled
- From: "Robert Karl Stonjek" <rstonjek@xxxxxxxxxxxxxx>
- Date: Thu, 25 May 2006 01:31:09 -0400 (EDT)
The Nucleosome Untangled
Histones serve as slates to a dizzying array of modifications, but
researchers are confident they can decipher the epigenetic puzzle.
BY BRENDAN MAHER
Roughly two meters of DNA gets packed into every cell nucleus in the human
body. In addition to stuffing all that information into a sphere 3 to 10
microns across, the proteins that perform this task must also ensure that in
each cell certain genes are constantly transcribed, while others lie ready,
and other regions remain dormant, practically inaccessible. Within this
cramped, chaotic space, an army of proteins must manage cellular
information, decide cell fate with a moment's notice and maintain it, often
passing that fate to daughter cells.
This regulation takes place in the context of the histone proteins. Two each
of the four standard histones - H3, H4, H2A, and H2B - join together to form
an octameric nucleosome, a spool around which roughly 146 nucleotides wind
in a near double loop. By no means inert packing material, the nucleosome
serves as a slate for a rich variety of modifications or "marks" that appear
to play a role in managing the genome. Acetylation, methylation,
phosphorylation, ubiquitination, sumoylation - the list of modifications
grows monthly. Researchers have mapped as many as 50 different marks to
specific amino acid residues on the histones' highly conserved N-terminal
tails and elsewhere on the molecules, says Thomas Jenuwein from the Research
Institute of Molecular Pathology in Vienna. "One of the challenges, I think,
is to identify all of the modifications that exist," says Tony Kouzarides,
of the Wellcome Trust/Cancer Research UK Gurdon Institute.
Full Text at TheScientist
http://www.the-scientist.com/article/daily/23392/
Posted by
Robert Karl Stonjek
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