derepresses

Derepression is the process by which gene expression that was previously repressed becomes active due to the removal or inactivation of a repressive constraint. In this sense, it is the lifting of repression and a shift toward transcriptional activity. Derepression can occur when the repressor is inactivated, degraded, or displaced from the DNA, or when signals counteract repressive mechanisms.

In prokaryotes, repression often involves a repressor protein binding to an operator and blocking RNA polymerase. Derepression occurs when an inducer molecule binds the repressor, causing a conformational change that prevents DNA binding. This enables transcription of the operon or gene. Other routes include anti-repressor actions that relieve repression or genetic mutations that disrupt repressor function or operator sites.

In eukaryotes, repression can be mediated by chromatin-based mechanisms, such as repressive histone marks or Polycomb group complexes. Derepression may involve chromatin remodeling, histone acetylation, DNA demethylation, or recruitment of transcriptional activators that override repressive states, leading to gene activation.

Examples abound in biology. The lac operon in Escherichia coli is classically derepressed by allolactose, which inactivates the LacI repressor and permits transcription when other conditions permit it. In yeast, GAL genes are derepressed in the presence of galactose via relief of GAL80-mediated repression on GAL4. Derepression plays a key role in developmental gene regulation, metabolism, and adaptive responses.

Overall, derepression reflects the dynamic regulation of gene expression in response to cellular signals and environmental conditions.