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Histone Modifications and
Transcriptional Activation
By
Anna Purna
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http://purnasrinivas.weebly.com
29th July 2011
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Histone Modifications

These modifications make a region
of gene either transcriptionally
active or inactive.
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Acetylation




Addition of acetyl
groups (CH3CO-)
to lysines.
Acetylation 
DNA is stopped
from getting
further condensed
Active
transcription of the
genes takes place
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Phosphorylation


Addition of phosphate
groups to serines and
threonines.
Serine 10 of Histone H3
gets specifically
phosphorylated during
mitosis and meiosis
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Methylation


Addition of
methyl groups
to lysines and
arginines.
This either
stimulates or
inhibits gene
transcription at
that region.
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Methylation



Methylation of histone H4 on R4 (arginine residue at
the 4th position) →→ opens the chromatin structure
→→ leading to transcriptional activation
Methylation of histone H3 on K4 and K79 (lysines
residues at the 4th and 79th position) →→ opens
the chromatin structure →→ leading to
transcriptional activation
Methylation of histone H3 on K9 and K27 (lysines
residues at the 9th and 27th position) →→
condenses the chromatin structure →→ leading to
transcriptional inactivation
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Ubiquitination



Ubiquitin (Ub) is a 76-amino acid
protein that is ubiquitously
distributed and highly conserved
throughout eukaryotic organisms.
Ubiquitination of H2A –
Transcriptional inactivation
Ubiquitination of H2B Transcriptional activation
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