Question

How do histones control gene expression, yet genes also control histones?

Short answer

Histones control gene expression through their binding to DNA. Tightly bound histones prevent transcription and gene expression, while loosely bound histones allow it. Conversely, genes control histones through the process of acetylation and deacetylation. Environmental or biological factors can trigger gene expression that signals these modifications to the histones.

Step-by-step solution

Understanding Histones

Histones are alkaline proteins found in eukaryotic cell nuclei, which package and order the DNA into structural units called nucleosomes. They play a central role in gene regulation as the adjustments of these histones can enable or disable gene expression.

How Genes Control Histones

Gene expression can influence changes to the histones. Different biological factors can cause genes to signal modifications to histones, such as the addition or removal of acetyl groups - a process known as acetylation and deacetylation. This affects the structure of the histones, which subsequently impacts their ability to bind to DNA and, thus, control gene expression.

How Histones Control Gene Expression

Histones can impact gene expression by adjusting their binding to DNA. When the histones are tightly bound to the DNA (a process often induced by deacetylation), they limit the access of transcription factors and RNA polymerase to the DNA, which stops the process of transcription and suppresses gene expression. Alternatively, if the histones are loosely bound or not bound to the DNA (often induced by acetylation), transcription can occur because the transcription machinery has access to the DNA, leading to gene expression.