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Regulation of Gene Expression in Molecular Biology

• Regulon refers to a group of genes or operons that are coordinately regulated, whether spatially distant or not.
• Transcriptional regulation can be negative, where repressor proteins inhibit transcription by binding to the promoter, or positive, where activator proteins recruit RNA polymerase to initiate transcription.
• DNA looping, facilitated by transcription activators and architectural regulators, can bring distant regulatory sites together to enable transcription.
• The bacterial Lac repressor, made of four subunits, binds distant DNA sites to form a DNA loop.
• Insulators, present in prokaryotes and eukaryotes, block unintended effects of DNA looping and control gene expression.
• Effectors, small molecules, can bind activators or repressors, causing conformational changes that increase or decrease transcription.
• Effectors can inactivate a repressor, enabling transcription, or activate a repressor, shutting down transcription.
• Effectors can also inactivate or enable activators to stimulate transcription.
• Global regulation of gene expression involves coordinated expression of several genes in response to stress, occurring in prokaryotes and eukaryotes.
• Coordinated transcription of several genes in the SOS system involves the RecA protein and LexA repressor protein in response to DNA damage.
• In the SOS system, DNA damage induces autocleavage of LexA repressor, facilitated by RecA protein, leading to the induction of the SOS response.
• DNA damage creates sites of single-stranded DNA, which are bound by RecA protein, and their association facilitates the destruction of LexA and induction of the SOS response.