1. Chromatin remodeling is the process by which chromatin structure is dynamically modified to allow access of DNA for processes like transcription. 2. There are two main types of chromatin remodeling - covalent histone modification and ATP-dependent chromatin remodeling complexes. 3. ATP-dependent complexes use energy from ATP hydrolysis to move, eject, or restructure nucleosomes, allowing access to DNA. 4. Examples of chromatin remodeling complexes include SWI/SNF, ISWI, CHD, and INO80 families, which have different activities like nucleosome sliding or histone variant exchange.

1. Mr. Balaji S. Thorat
Regd. No: ADPM/15/ 2418
Discipline: Genetics & Plant breeding.
Dept. : Agrl. Botany, College of Agriculture, Dapoli.

2. Introduction:
Definition: Chromatin remodeling is the enzymeassisted process to
facilitate access of nucleosomal DNA by remodeling the structure,
composition and position of nucleosomes.
Chromatin remodeling is the dynamic modification of chromatin
architecture to allow access of condensed genomic DNA to the
regulatory transcription machinery proteins, and thereby control gene
expression.

3. Why do Cells Require chromatin Remodeling
 Binding of the DNA to the histone octamer and the bending
of the molecule on the protein surface present a strong
barrier to sequence specific recognition of the nucleosomal
DNA molecule.
 That’s why the packaging of DNA into nucleosomes and
higher order structure is generally inhibitory to all kind of
DNA dependent processes.
 To overcome DNA sequence accessibility problems, cells
have developed mechanisms to open higher order structures
of chromatin and to disrupt nucleosomes allowing the
binding of sequence specific regulators.

4. Types Of Chromatin Remodeling
There are two types namely,
1. Covalent histone modification.
2. ATP dependent chromatin remodeling
1. Covalent histone modification:
Specific protein complexes, known as Histone- Modifyieng
complexes catalyze addition or removal of various chemical
elements on histones.

6. 2. ATP dependent chromatin remodeling
ATP dependent chromatin remodeling complexes regulate
gene expression by either moving, ejecting or restructuring
nucleosomes.
 These protein complexes have a common ATPase domain
and energy from the hydrolysis of ATP allows these
remodeling complexes to reposition (slide, twist or loop)
nucleosomes along the DNA, expel histones away from DNA
or facilitate exchange of histone variants thus creating
nucleosome free regions of DNA for gene activation.

7. Chromatin
Remodeling
Complexes
SWI/SNF
family
ISWI
family
CHD familyINO80
family

8. 1. SWI/SNF family
remodelers.
 The SWI/SNF (switching defective/sucrose nonfermenting)
family remodelers were initially purified from Saccharomyces
cerevisiae and are composed of 8 to 14 subunits.
SWI/SNF remodelers are highly conserved across different
species, including Saccharomyces cerevisiae, Drosophila
melanogaster and Homo sapiens.
This family has many activities, and it slides and ejects
nucleosomes at many loci and for diverse processes but lacks
roles in chromatin assembly.

9. 2. ISWI family
remodelers.
The ISWI (imitation switch) family remodelers contain 2 to 4
subunits.
 Most eukaryotes build multiple ISWI family complexes using
one or two different catalytic subunits, with specialized
attendant proteins.
Specialized attendant proteins impart many domains, including
DNA-binding histone fold motifs, plant homeodomain (PHD),
bromodomains , and additional DNA-binding motifs.

10. 3. CHD family remodelers
The 1st CHD (Chromodomain, Helicase, DNA binding) family
remodeler identified was Mi-2, combine 1 to 10 subunits and
were first purified from Xenopus laevis.
Characteristic feature include two tandemly arranged chromo -
domains on the N terminus of the catalytic subunit.
The catalytic subunit is monomeric in lower eukaryotes but can
be in large complexes in vertebrates .
Certain CHD remodelers slide or eject nucleosomes to promote
transcription.

11. 4. INO80 family remodelers.
The INO80 (inositol requiring 80) family remodelers contain more than 10 subunits,
include the SWR1-related complexes and were initially purified from S. cerevisiae.
 The defining feature is a “split” ATPase domain, with a long insertion present in the
middle of the ATPase domain, to which the helicase-related (AAA-ATPase) Rvb1/2
proteins and one ARP protein bind.
INO80 has diverse functions, including promoting transcriptional activation and
DNA repair. Although highly related to INO80, SWR1 is unique in its ability to
restructure the nucleosome by removing canonical H2A-H2B dimers and replacing
them with H2A.Z-H2B dimers, thereby inserting the histone H2A variant H2A.Z.

12. Domains, proteins, and modifications that
regulate remodelers

13. Shared characteristics of chromatin
remodeling complexes:
 They bind to nucleosomes
 They are DNA-dependent ATPases
 They recognize histone modifications
 Their ATPase activity can be regulated
 They interact with other proteins

14. One
• Nucleosome Sliding
Two
• Ejection of histone octamers
Three
• Removal of H2A-H2B dimers
Four
• Replacement of dimers

15. Loop formation mechanism during chromatin remodeling

17. 1. Nucleosome Sliding

18. Removal of histones from the DNA

19. Replace core histones with variant histones.

20. CHROMOSOMAL PROCESSES
REQUIRING REMODELERS
1. Chromatin Assembly :

21. 2. Dosage Compensation :
 In Drosophila dosage compensation, the hyperacetylation at
H4K16 of the male X by dMOF, a component of the Drosophila
dosage compensation complex .
 Acetylation of H4K16 inhibits chromatin compaction in
two ways: H4K16ac inhibits fiber formation and reduces,
ISWI remodeling activity. The result is a finely tuned balance:
H4K16ac promotes the twofold increase in transcription and
impaired ISWI function

22. 3. DNA Repair
 DNA lesions occur often and threaten genome integrity,
requiring a rapid recognition of sites of damage within
chromatin.
 However, chromatin actually facilitates repair, with one of the
fastest cellular responses to damage being the phosphorylation
of serine 129 of H2A in yeast or serine 139 of H2A.X in
vertebrates.
 This phosphorylation helps recruit DNA repair factors as well
as chromatin remodelers of the SWI/SNF and INO80 families,
likely to facilitate access to DNA ends for repair enzymes.

23. 4.Chromosome Segregation
 Remodeler plays an important role in chromosome segregation.
 hATRX a SNF2-related protein, binds to centromeric heterochromatin at
meiotic onset, promoting a bipolar meiotic spindle and proper chromosome
alignment .
 In humans, an hSNF2H family remodeler mediates cohesin loading. Also, the
SWI/SNF family remodeler yRSC is constitutively present at the centromeres
and promotes proper kinetochore function and chromosome segregation .
 yRSC associates with chromosome arms and interacts directly with cohesin to
preserve chromosome cohesion and promote proper chromosome segregation.

24. Case studies

25. Organism studied : Drosophila melanogaster
Chromosomes Studied: Male X chromosome, polytene chromosome,
Autochromosomes of neuroblast cells
Chromatin Remodeling Factor Involved: ISWI

26.  Interactions between histone-modifying and
chromatin remodeling enzymes can have profound
effects on higher order chromatin structure as
illustrated by recent studies of the Drosophila
chromatin-remodeling factor ISWI.
 ISWI functions as the ATPase subunit of at least
three distinct chromatin-remodeling complexes: ACF,
CHRAC, and NURF.
 The loss of Iswi function leads to the dramatic
decondensation of a specific chromosome: the male X

27. Figure 1. ISWI Plays a Global Role in Chromosome Compaction In
Vivo.
Polytene chromosomes( A,B),
X Chromosome( C,D,E,F)
chromosomes of neuroblast cells

28. 3. Loss of ISWI Results in loss of Histone H1
Assembly

29. Inference:
ISWI is a global regulator of polytene chromosome
structure.
ISWI is required for the generation, maintenance of
higher order chromatin structure in diploid cells.
ISWI plays relatively global roles in transcriptional
activation and repression in vivo.
ISWI Promotes the Association of the Linker
Histone H1 with Chromatin

30.  The conserved histone variant H2AZ has an important role in the regulation of
gene expression.
Swr1, a Swi2/Snf2-related adenosine triphosphatase, is the catalytic core of a
multisubunit, histone-variant exchanger that efficiently replaces conventional
histone H2A with histone H2AZ in nucleosome arrays.
 Swr1 is required for the deposition of histone H2AZ at specific chromosome
locations in vivo and Swr1 and H2AZ commonly regulate a subset of yeast genes.
 These findings define a previously unknown role for the adenosine triphosphate–
dependent chromatin remodeling machinery

31. Material and Methods
Organism studied: Saccharomyces cerevisiae
Method: Immuno purification from whole-yeast
extracts for the purification of native Swr1.
followed by SDS –PAGE and glycerol
gradient centrifugation.

32. SWR1 complex exchanges nucleosomal H2A with Htz1. (A)
SDS-PAGE and silver staining showing histones
retained on immobilized nucleosome arrays before (lane 1)
and after (lane 2) Htz1 transfer.

33. Inference:
 A multicomponent SWR1 complex containing H2AZ
(Htz1) indicates association between H2AZ and
SWR1
 Chromatin binding of Htz1 in vivo requires Swr1.
 SWR1 complex catalyzes replacement of H2A with
Htz1 in vitro.

34. CONCLUSION
 Chromosomal biology involves a dynamic balance between
genome packaging and genome access.
 Remodelers are needed to fully package the genome, to
specialize chromatin regions, and to provide regulated
DNA accessibility in packaged regions.
 Chromatin modifiers and remodelers work in concert to
direct nucleosome dynamics. Nucleosome determinants
and covalent modifications are recognized by remodelers
and may be used both for targeting and regulating the
remodeling reaction.

35. REFERENCES:
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 2. Corona DF, Tamkun JW. 2004., Multiple roles for ISWI in
transcription, chromosome organization and DNA replication.
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SA, et al. (2007) ISWI regulates higher-order chromatin structure
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

36. 36
Thank You..