Histones are positively charged proteins that DNA wraps around to form nucleosomes, the basic unit of chromatin. The four core histones, H2A, H2B, H3, and H4, contain high proportions of lysine and arginine amino acids. H2A, H2B, and H1 contain more lysine while H3 and H4 contain more arginine. Histone modifications like acetylation and phosphorylation can regulate gene expression by altering chromatin structure and accessibility to transcription proteins. Acetylation reduces the positive charge of histones and weakens their interaction with DNA, allowing transcription. Phosphorylation also weakens histone-DNA interactions and influences chromatin structure and cellular processes like DNA

1. HISTONES
Ankita Behera
M.Sc Microbiology
St. George College of Management & Science
Bengaluru North University

5.  Histones contain a large proportion of the
positively charged amino acids, lysine and
arginine in their structure.
DNA wraps around histones and they also
play a role in GENE REGULATION.

9. H2A{CONTAIN MORE LYSINE:-
◦ H2A packages DNA molecules into chromatin ,the packaging process
will effect GENE Expression.
◦ They vary often by only a few amino acids.
◦ 10.9% of lysine.
◦ It plays a major role in determining the overall structure of chromatin
and has been found to regulate gene expression.
◦ Molecular weight is 13,960.

10. H2B {contain more lysine}:-
◦ It is also involved with the structure of the nucleosome of the
“BEADS ON A STRING” structure.
◦ Its molecular weight is 13,774.
◦ 16% of lysine.
◦ It is also found to regulate GENE EXPRESSION.

11. H3{CONTAIN MORE ARGINE}:-
◦ It features a main Globular domain and a long N-terminal tail.
◦ It is an important protein in the merging field of epigenetics , where
its sequence variants and variable modification states are thought to
play a role in the Dynamic and long term regulation of genes.
◦ It is in the structure of chromatin in eukaryotic cells .
◦ Molecular weight is 15,273.

12. H4{CONTAIN MORE ARGINE}:-
◦ Molecular weight is 11,236.
◦ It is the structural component of the nucleosome and is subject to
covalent modification , including acetylation and methylation which
may alter expression of genes located on DNA associated with its
parent histone octamer.
◦ Also involved in the structure of chromatin in Eukaryotic cells.

14. H1 {highest lysine/arginine ratio}:-
◦ It is not part of the nucleosome core particle instead binds to the
linker DNA is reffered as “LINKER HISTONE”.
◦ It is half as abundant a sother histones which is consistent with the
finding that only one molecule of H1 can associate with a
nucleosome.

15. Function of the histone protein in a
chromosome:-
◦ The DNA is housed in chromosomes in the form of nucleosomes.
◦ Positively charged histones are linked with negatively charged
phosphate group of DNA.
◦ It is the basic unit of chromosome or chromatin fibre.

18. It has been proposed that these
modifications results in a “code” which
can be read by proteins involved in
GENE EXPRESSION and other DNA
translation.

20. ACETYLATION
◦ Acetylation provides binding sites for a number of proteins with an approx.100
amino acids sequence most called “BROMODOMAIN”.
ACETYLATION DEACETYLATION
• HISTONE ACETYLATION • HISTONE DEACETYLATION
• Enzyme responsible for it are
“HISTONE ACETYL
TRANSFERASE”(HATs).
• Enzyme responsible for it are
“HISTONE
DEACETYLASES”(HDACs).
• Allow transcription • Repress transcription.
• Reduces positive charge and weak the
interaction of histones with DNA.
• Increases interaction of DNA and
histones.
• Adda acetyl groups to histone tails. • Removes acetyl groups from histone tails.

25. phosphorylation
◦ It is the addition of phosphate group to a molecule.
◦ It is catalyzed by various proteins “KINASES”where as phosphatase mediate
removal of phosphate group.
◦ It make the histone more negative which weakens the packing ability of histones.
◦ Phosphorylation of histones is particular H2AX has a role in DNA damage
response and DNA repair .
◦ Phosphorylation of H3S10 was linked to chromosome relaxation and
segregation.
◦ Although information is limited and is clear they can influence chromatin
structure and have a significant impact on cellular activity

26. THANK YOU