Chromatin Remodeling

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Chromatin Remodeling

• Presentation prepared by Cassidy Zanko

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Why Must We Remodel Our Chromatin?!

• Our DNA is so tightly compacted into chromosomes
  that many important nuclear processes cannot take
  place because direct access is blocked. These
  processes include transcription, replication, DNA
  repair and homologous recombination.
• In order to allow for proper interactions between
  transcription factors or RNA polymerases and our
  DNA, chromatin must be altered or remodeled and
  therefore, made accessible.
• This is one example of epigenetic changes
  changes that may affect our phenotypes without
  directly affecting our DNA.

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How Does Chromatin Get Remodeled?

• Two general mechanisms are used to remodel
  chromatin
• Chemical modification of histones
• ATP-Dependent chromatin remodeling
• Our chromatin structure can only be regulated by
  first chemically modifying the histone proteins
  that interact with our compacted DNA (as shown in
  previous slide)
• Histone proteins can undergo modification by
  site-specific
• acetylation (addition of an acetyl group by
  histone acetyltransferase (HAt)),
• methylation (addition of a methyl group by
  histone methyltransferases), and
• phosphorylation (addition of a phosphate group)
• ATP-dependent chromatin remodeling factors
  (ADCRFs) use energy from ATP hydrolysis to alter
  the structure or positioning of nucleosomes (and,
  hence, chromatin) rendering the chromatin dynamic
  and, therefore, active!
• ADCRFs that have been studied include SNF2 in
  yeast, ISWI in Drosophila, amd CHD1 in mice.
• Homologous SWI/SNF proteins have been found in
  mammals

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Take Home Message The chromatin remodeling
mechanisms discussed counterbalance the repressed
chromatin and enable important nuclear processes
to take place, ultimately facilitating expression
of our genome.
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References

• Fyodorov, Dmitry and Kadonaga, James. The Many
  Faces of Chromatin Remodeling. Molecular Biology,
  University of California, San Diego. Online. 11
  September 2001. http//linkinghub.elsevier.com/ret
  rieve/pii/S0092867401004780
• Jakubowski, Dr. Binding and the Control of Gene
  Transcription. Biochemistry-Chapter 5-Binding.
  Online. 28 December 2006. http//employees.csbsju.
  edu/hjakubowski/classes/ch331/bind/olbindtranscipt
  ion.html
• Konev, A. Chromatin Remodeling by hSWI/SNF
  ATP-dependent complexes. Biocarta. Online.
  http//www.biocarta.com/pathfiles/h_hSWI-SNFpathwa
  y.asphistory
• Pictures
• http//www.stkate.edu/physics/Astrobiology/
• info.med.yale.edu/therarad/glazer/people.html
• http//faculty.jsd.claremont.edu/jarmstrong/images
  /crcactivity.gif