Genetics and Genomics: Nucleosome, Lampbrush chromomsome and Histone proteins

1. By: Dr. Sonia Goel
SGT University, Gurugram

2. Nucleosome
 A nucleosome is a section of DNA that is wrapped
around a core proteins. DNA forms a complex with
protein called chromatin.
 Chromatin is extended and viewed in microscope, the
structure resembles beads on a string. Each of beads is
called a nucleosome.
 Nucleosome is composed of set of eight proteins called
histones, which is also known as histone octamer.
 H2A, H2B, H3, H4 are the histone protein.

3. Contd...
 The chain of nucleosome is compacted further and form a
highly organized complex of DNA and protein called a
chromosome.
 The nucleosome core protein (NCP) consist of about 146
basepair of DNA wrapped in 1.67 left handed superhelical
turns around the histone octamer.
 Adjecent nucleosome are joined by a strecth of free DNA
termed linker DNA.
 Whole structure make a cylinder of diameter 11nm and
height of 5.5 nm.

5. Lampbrush Chromosome
 Lampbrush Chromosome were discovered in
salamander egg cell by Flemming in 1882. LPC's
were identified in shark egg cell and identified by
Ruckert in 1982.
 LPC'S are special form of chromosome found in the
growing oocytes of animals, except mammals.
 Chromosome transform into LPC form during the
diplotene stage of meiotic prophase due to the
active transcription of many genes.

6. Lampbrush Chromosome Transcription
1. Transcriptional activity of gene can only be assessed
using molecule methods that consist detecting the
amount of the transcription process.
2. Higher transcription activity of microchromosome is
observed due to greater density of gene.
3. The morphology and transcription activity of LPC'S
depending on the reproductive cycle. They also undergo
seasonal changes.
4. During, summer animals are most active, while in
winter animals are less active.

7. Contd...
1. Lampbrush Chromosome show the possible way
of the gene amplification.
2. The Lampbrush Chromosome loops are used to
studying transcription.

9. Histones: Types & Their Role
 Histones are highly alkaline proteins found in
eukaryotic cell nuclei that package the DNA into
structural units called nucleosome.
 Histones form dimers and tetramers. Dimers have two
and tetramer have four histones.
 H2A and H2B histones called dimer and H3 and H4
histones called tetramer.
 Basically, there are five types of histones .

10. Types & Their Role
 H2A:- is important for packaging DNA into chromatin. The
packaging also effect the gene expression. H2A also play
important role in determining the overall structure of
chromatin.
 H2B:- involved with the structure of the nucleosome of the
'beads on a string' structure.
 H3:- also involved in the structure of chromatin in
eukaryotes cells and featuring main globular domain and a
long N-terminal tail.
 H3 also play a role in dynamic and long term regulation of
gene.

11. Contd...
 H4:- H4 is a structural components of the nucleosome
and is subject to covalent modification including
acetylation, methylation.
 H5:- H5 histone are individual protein involve in the
packaging of specific region of DNA.

12. Histone Chaperones
 Histone Chaperones are the architects of epigenetic
inheritance. They are responsible for deposition of histones
on DNA to form chromatin and their removal from DNA to
enable genomic process to occur.
 Histones are separate group of protein differing in
structure and mode of interaction with histones.
 The function of histone Chaperones is nucleoplasm in the
prevention of histone-DNA aggregation during
nucleosome assembly.
 Nap1 help in newly synthesized histones from the
cytoplasm to the nuclus.
 NASP act as histone reserviour and regulate histone supply.

13. Contd...
 RbAp46 & AsP1 regulate the enzymatic activity of
histon modifying enzyme serving to bridge interaction
between histones and histones modifying enzyme.