Small Molecule‐Based Conditional Gene Regulation: Advances and Applications

The precise, temporal, and reversible control of gene expression using small molecule ligands is crucial for understanding complex cellular functions and is rapidly advancing the field of synthetic biology. Small molecule‐mediated conditional gene regulation has widespread applications, including bio‐manufacturing, cellular reprogramming, gene therapy, and genome editing. The conditional regulatory systems act as molecular switches where a small molecule ligand interacts with target biomolecules (DNA, RNA, or proteins) and either induces the dimerization or recruitment of components, causes steric hindrance to block a process, or allosterically alters the target's functional conformation to modulate the gene expression over orders of magnitude in optimized contexts. This review provides a comprehensive mechanistic survey of these systems at the transcriptional, post‐transcriptional, translational, and post‐translational levels, highlighting recent innovations and applications across bacteria to human cells. It also discusses key challenges, including achieving high ligand binding (affinity), effective delivery (permeability), minimal side effects (toxicity), and low background activity (leakiness), that need to be addressed to fully unlock the potential of these regulatory systems for biomedical applications.