Histone
acetylation
Histone acetylation, another important mechanism of epigenomic change,
relates to folding of
histones, the protein spindles around which DNA is wrapped. Patterns of histone acetylation are also part of epigenomic memory.
Histones regulate gene expression by affecting the structure of chromatin and thus affect the ability of transcriptional activators and repressors
to access regulatory DNA sequences. i.e. an unfolded (acetylated) histone provides more
physical access to a gene promoter sequence
than does a folded (deacetylated) histone.
Thus, via relaxing chromatin structure, gene expression is stimulated by
HATs which allow transcription
factors access to get to DNA . On the other hand, deacetylation of histones by HDACs
promotes chromatin condensation and represses gene expression. Histone deacetylation, like DNA methylation, can result in gene
silencing.
Posttranslational modifications
of histones is thought to be an important part of the epigenetic "code"
that determines patterns of cellular gene expression.
The mTOR longevity signaling pathway is affected in
normal and cancer cells by HATs.