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Controlling Chromatin Structure

Controlling Chromatin Structure. Chapter 30. 30.2 Chromatin Can Have Alternative States. Chromatin structure: is stable cannot be changed by altering the equilibrium of transcription factors and histones. Figure 30.2. 30.3 Chromatin Remodeling Is an Active Process.

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Controlling Chromatin Structure

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  1. Controlling Chromatin Structure Chapter 30

  2. 30.2 Chromatin Can Have Alternative States • Chromatin structure: • is stable • cannot be changed by altering the equilibrium of transcription factors and histones Figure 30.2

  3. 30.3 Chromatin Remodeling Is an Active Process • There are several chromatin remodeling complexes that use energy provided by hydrolysis of ATP. Figure 30.3

  4. The SWI/SNF, RSC, and NURF complexes all: • are very large • they share some common subunits • A remodeling complex does not itself have specificity for any particular target site. • It must be recruited by a component of the transcription apparatus. Figure 30.5

  5. 30.4 Nucleosome Organization May Be Changed at the Promoter • Remodeling complexes are recruited to promoters by sequence-specific activators. • The factor may be released once the remodeling complex has bound. Figure 30.6

  6. The MMTV promoter requires a change in rotational positioning of a nucleosome to allow an activator to bind to DNA on the nucleosome. Figure 30.7

  7. 30.5 Histone Modification Is a Key Event • Histones are modified by: • methylation • acetylation • phosphorylation Figure 30.8

  8. 30.6 Histone Acetylation Occurs in Two Circumstances • Histone acetylation occurs transiently at replication. Figure 30.12

  9. Histone acetylation is associated with activation of gene expression. Figure 30.13

  10. 30.7 Acetylases Are Associated with Activators • Deacetylated chromatin may have a more condensed structure. • Transcription activators are associated with histone acetylase activities in large complexes. Figure 30.14

  11. Histone acetylases vary in their target specificity. • Acetylation could affect transcription in a quantitative or qualitative way.

  12. 30.8 Deacetylases Are Associated with Repressors • Deacetylation is associated with repression of gene activity. • Deacetylases are present in complexes with repressor activity. Figure 30.16

  13. 30.9 Methylation of Histones and DNA Is Connected • Methylation of both DNA and histones is a feature of inactive chromatin. • The two types of methylation event may be connected.

  14. 30.10 Chromatin States Are Interconverted by Modification • Acetylation of histones is associated with gene activation. • Methylation of DNA and of histones is associated with heterochromatin. Figure 30.17

  15. 30.11 Promoter Activation Involves an Ordered Series of Events • The remodeling complex may recruit the acetylating complex. • Acetylation of histones may be the event that maintains the complex in the activated state. Figure 30.18

  16. 30.12 Histone Phosphorylation Affects Chromatin Structure • At least two histones are targets for phosphorylation, possibly with opposing effects.

  17. 30.13 Some Common Motifs Are Found in Proteins That Modify Chromatin • The chromo domain is found in several chromatin proteins that have either activating or repressing effects on gene expression. • The SET domain is part of the catalytic site of protein methyltransferases. • The bromo domain: • is found in a variety of proteins that interact with chromatin • is used to recognize acetylated sites on histones.

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