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🔬general biology i review

H3K27me3

Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025

Definition

H3K27me3 refers to the trimethylation of lysine 27 on histone H3, which is a crucial epigenetic modification that plays a significant role in gene regulation within eukaryotic cells. This modification is often associated with transcriptional repression, marking regions of chromatin that are silenced or not actively expressed. Understanding H3K27me3 is essential as it reflects how genes can be turned off and is involved in developmental processes, cellular differentiation, and the maintenance of cell identity.

5 Must Know Facts For Your Next Test

  1. H3K27me3 is established by the Polycomb Repressive Complex 2 (PRC2), which is critical for maintaining gene repression during development.
  2. The presence of H3K27me3 is often found in regions of the genome that are involved in developmental genes and cell type specification.
  3. Dysregulation of H3K27me3 can lead to various diseases, including cancer, where inappropriate gene expression patterns can occur.
  4. This modification is part of a broader set of histone modifications that work together to regulate gene expression and chromatin structure.
  5. H3K27me3 can be dynamically removed or added, allowing cells to respond to developmental cues and environmental changes by turning genes on or off.

Review Questions

  • How does H3K27me3 contribute to gene regulation in eukaryotic cells?
    • H3K27me3 contributes to gene regulation by marking specific regions of chromatin for transcriptional repression. When lysine 27 on histone H3 is trimethylated, it signals that the associated genes should be silenced. This modification is critical during development and helps maintain the identity of different cell types by ensuring that genes needed for one cell type are turned off in others.
  • Discuss the role of Polycomb Repressive Complex 2 (PRC2) in the establishment of H3K27me3 and its implications for cellular differentiation.
    • Polycomb Repressive Complex 2 (PRC2) is essential for the trimethylation of H3K27, directly influencing gene silencing. When PRC2 adds methyl groups to this specific lysine residue, it helps maintain gene repression over time. This function is particularly important in cellular differentiation, as it ensures that developmental genes are appropriately silenced in certain cell types while allowing expression in others, shaping the overall fate of cells during development.
  • Evaluate the consequences of aberrant H3K27me3 levels in relation to disease states such as cancer.
    • Aberrant levels of H3K27me3 can have serious consequences in disease states like cancer. When H3K27me3 is misregulated, it can lead to inappropriate activation or repression of genes that control cell growth and division. For example, if tumor suppressor genes are silenced due to excessive H3K27me3 modifications, cancer cells may proliferate uncontrollably. Understanding these changes opens avenues for targeted therapies aimed at reversing such epigenetic modifications to restore normal gene expression patterns.