derepression

Derepression is a biological process in which transcriptional repression is lifted, allowing gene expression to resume or increase. In genetics, repression typically involves a repressor protein that binds to regulatory DNA sequences and blocks transcription. Derepression occurs when the repressor is inactivated, displaced, degraded, or its effects are counteracted by an inducer or signaling pathway. In epigenetics, derepression can also describe the reversal of repressive chromatin states or DNA methylation, enabling chromatin remodeling and transcriptional activation.

Mechanisms include ligand-induced inactivation of repressors; proteolysis of repressor proteins; post-translational modifications that reduce repressor affinity; recruitment of chromatin remodelers and histone-modifying enzymes that remove repressive marks; and DNA demethylation. The result is a transition from a repressed to an active transcriptional state at specific genes or loci.

Examples include the bacterial lac operon, which is derepressed when allolactose binds the lac repressor, allowing expression of enzymes for lactose utilization. In eukaryotes, development and differentiation often require derepression of lineage-specific genes that are kept silent by chromatin modifiers and repressive histone marks; environmental cues can similarly trigger derepression of stress-response or metabolic genes. Aberrant derepression—such as inappropriate activation of silenced genes—can contribute to disease, illustrating the importance of controlled derepression in gene regulation.

In summary, derepression refers to the lifting of repression, enabling gene activation in response to developmental, environmental, or cellular signals.