 | Introduction
The eukaryotic nucleus is a dynamic environment of
functionally associated nucleic acids, cytoskeletal
structure, and maintenance and signaling proteins.
The genetic component of the nucleus is packaged as
chromatin. Chromatin is a composite of nucleosomal
units, each nucleosome formed from the spooling
of approximately 147 base pairs of DNA around an
octamer of histone subunits (two each of H2A, H2B,
H3, and H4). The structure of chromatin varies from
tightly compacted heterochromatin, whereby DNA
sequences are inaccessible to transcriptional complexes,
to an uncoiled euchromatin structure that allows for
regulated interaction of proteins with DNA. The structure
of chromatin and control of gene expression from its
packaged DNA is influenced by epigenetic mechanisms,
involving many enzymatic activities that dynamically
modify histones and other proteins, in response to
cellular cues. |
