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Depiction of some aspects of the chromatin surrounding the CpG sites (open lollipops) in a CpG island in a promoter of a normally unmethylated gene
(top panel) and actively transcribed gene versus the chromatin in this region of the same gene when hypermethylated (black lollipops) and transcriptionally
silenced (red X at transcription start site) in a tumor cell (bottom panel). The key aspect of the chromatin for the transcriptionally active (arrow)
unmethylated promoter is occupancy by widely spaced nucleosomes composed of histone complexes in which key residues in the tails of histone H3 are
in the acetylated state (green ovals) and the tails of histone H3 are methylated at lysine 4. The region is accessible to key components of the gene
transcription apparatus including primary transcription factors (TF), proteins with histone acetyltransferase activity (HAT) that maintain the histones in an
Source: DNA Methylation and Epigenetic Silencing of Genes in Cancer, The Online Metabolic and Molecular Bases of Inherited Disease
acetylated state, and transcriptional coactivators (CoA) that also may have HAT. Flanking regions to either side of the unmethylated CpG island contain
Citation: Valle
D, regions
Beaudetare
AL,embedded
VogelsteininB,chromatin
Kinzler KW,
AntonarakisofSE,
Ballabio A, Gibson
K, Mitchell
The Online Metabolic
Molecular
methylated cytosines.
These
characteristic
transcriptionally
silenced
regionsG.
characterized
by bindingand
of MBPs
to
Bases
of
Inherited
Disease;
2014
Available
at:
http://mhmedical.com/
Accessed:
May
11,
2017
the methylated sites (black circles) and nucleosomes that are more tightly compacted and have deacetylated histones (red ovals). The MBPs are part of
Copyright
2017 McGraw-Hill
Education.
All rights reserved
complexes that
contain©HDACs,
which facilitate
the deacetylated
state of the histones. The apparatus for DNA methylation, the DNA methyltransferases,
and their complexes with transcriptional corepressors and HDACs have access to the flanking areas but not to the CpG island promoter region within the