Nucleosome repositioning

Definition

Nucleosome repositioning refers to the dynamic movement of nucleosomes along DNA, altering the accessibility of specific genomic regions for transcription factors and other regulatory proteins. This process plays a crucial role in the regulation of gene expression by allowing or restricting access to DNA sequences that control transcription, thereby influencing cellular functions and developmental processes.

5 Must Know Facts For Your Next Test

1. Nucleosome repositioning can be triggered by various signaling pathways and environmental cues, allowing cells to respond to changes rapidly.
2. The repositioning can lead to either the exposure or occlusion of promoter regions, thereby influencing whether genes are activated or silenced.
3. ATP-dependent chromatin remodelers play a key role in facilitating nucleosome repositioning by using energy from ATP hydrolysis to alter nucleosome structure and location.
4. Nucleosome positioning is not static; it is part of a dynamic process that integrates signals from both internal cellular states and external environmental factors.
5. Alterations in nucleosome positioning have been linked to various biological processes, including cell differentiation, development, and responses to stress.

Review Questions

• How does nucleosome repositioning influence gene expression in eukaryotic cells?
  • Nucleosome repositioning influences gene expression by changing the accessibility of DNA sequences for transcription factors and other regulatory proteins. When nucleosomes move away from promoter regions, the associated genes become more accessible for transcription initiation. Conversely, if nucleosomes position themselves over promoter sites, they can block access and prevent gene activation. This dynamic movement is essential for regulating when and how genes are expressed in response to various signals.
• Discuss the mechanisms by which ATP-dependent chromatin remodelers contribute to nucleosome repositioning.
  • ATP-dependent chromatin remodelers utilize the energy derived from ATP hydrolysis to alter nucleosome structure and position. They can slide nucleosomes along the DNA strand, evict them entirely, or even dimerize them to create more open chromatin configurations. These actions enable the remodeling complexes to make specific genomic regions accessible or inaccessible for transcription factors, thereby controlling gene expression. This mechanistic action is crucial for adapting cellular responses during processes like differentiation and development.
• Evaluate the implications of improper nucleosome repositioning on cellular functions and disease development.
  • Improper nucleosome repositioning can lead to misregulation of gene expression, which may result in abnormal cellular functions and contribute to disease development. For example, if nucleosomes fail to reposition correctly during cell differentiation, it can lead to issues such as cancer or developmental disorders due to genes being incorrectly activated or silenced. Understanding these mechanisms provides insights into therapeutic approaches aimed at correcting epigenetic abnormalities that arise from faulty chromatin dynamics.

Related terms

Chromatin Remodeling: The process by which the structure of chromatin is altered to either expose or hide specific DNA sequences, often through the action of ATP-dependent chromatin remodeling complexes.

Histone Modification: The addition or removal of chemical groups to histone proteins, which can affect nucleosome positioning and influence gene expression patterns.

Transcription Factors: Proteins that bind to specific DNA sequences to regulate gene transcription, often requiring access to the DNA that is influenced by nucleosome positioning.