Histone acetyltransferase

Definition

Histone acetyltransferase (HAT) is an enzyme that adds acetyl groups to the amino acids of histone proteins, leading to changes in chromatin structure and gene expression. This modification plays a crucial role in epigenetic regulation by influencing the accessibility of DNA to transcriptional machinery, making it easier for genes to be expressed. HATs are also involved in the signaling pathways related to nuclear receptors, which help regulate a variety of physiological processes.

5 Must Know Facts For Your Next Test

1. HATs promote an open chromatin structure by neutralizing the positive charge of histones, which reduces their affinity for negatively charged DNA.
2. The action of HATs is often counterbalanced by histone deacetylases (HDACs), which remove acetyl groups and promote a closed chromatin state.
3. Different types of HATs can target specific histones and can be recruited by transcription factors to activate particular genes.
4. Histone acetylation not only influences transcription but also plays roles in DNA repair and cell cycle regulation.
5. Certain HATs are regulated by signaling pathways involving nuclear receptors, linking extracellular signals to changes in gene expression.

Review Questions

• How does histone acetyltransferase influence gene expression at the molecular level?
  • Histone acetyltransferase adds acetyl groups to histone proteins, which leads to a more relaxed chromatin structure. This relaxed state allows transcription factors and RNA polymerase easier access to DNA, thus facilitating the transcription process. By modifying histones, HATs play a significant role in determining which genes are expressed based on the cellular context.
• Discuss the interplay between histone acetyltransferases and nuclear receptors in regulating gene expression.
  • Histone acetyltransferases are often recruited by nuclear receptors that bind to specific hormone response elements in the DNA. Once bound, these receptors can attract HATs to specific genes, resulting in increased histone acetylation and enhanced transcription of target genes. This process exemplifies how external signals, like steroid hormones, can modulate gene expression through epigenetic mechanisms.
• Evaluate the implications of altered histone acetyltransferase activity in diseases such as cancer.
  • Altered activity of histone acetyltransferases can lead to abnormal patterns of gene expression associated with cancer development. For instance, overactive HATs may promote the expression of oncogenes or suppress tumor suppressor genes through excessive acetylation. Understanding these changes opens avenues for targeted therapies aimed at restoring normal epigenetic regulation, potentially offering new strategies for cancer treatment.

Related terms

Histones: Proteins that package and order DNA into structural units called nucleosomes, playing a key role in gene regulation.

Acetylation:

The process of adding an acetyl group to a molecule, such as histones, which can alter protein function and gene expression.

Nuclear Receptors: A class of proteins that regulate gene expression in response to steroid hormones and other signaling molecules.