DNA-binding regulators and cellular signals affect transcription.
Key knowledge
Regulatory proteins can activate or repress transcription through interactions with DNA and transcription machinery. Bacterial operons provide examples of coordinated regulation of several genes. Gene-expression control also occurs after transcription, so transcript abundance alone does not determine active protein abundance.
Conditions and scope
Operons are an example, not a universal organization of all genes.
Regulatory effects depend on organism, cell state and molecular context; eukaryotic regulation includes chromatin and additional processing stages.
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References
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Mary Ann Clark, Matthew Douglas and Jung Choi — OpenStax, Rice University2 sources
Regulatory proteins can activate or repress transcription through interactions with DNA and transcription machinery. Bacterial operons provide examples of coordinated regulation of several genes. Gene-expression control also occurs after transcription, so transcript abundance alone does not determine active protein abundance.
Transcription is one of several regulated expression stages.
Chemical modifications of DNA and associated proteins can affect how cells use genetic information without changing the underlying DNA sequence. Some regulatory states persist through cell division; inheritance across organismal generations is a separate, context-dependent question.
DNA-associated regulatory marks can affect expression without a sequence change.
Animal endocrine signals affect target cells through receptors. Some hormones act through cell-surface receptors and intracellular signalling pathways; others act through intracellular receptors that influence gene expression. A hormone's presence does not imply that every cell responds in the same way.
Some intracellular hormone receptors influence transcription.
In the E. coli lac example, a repressor and a cAMP-linked activator integrate lactose-related and glucose-related conditions to regulate transcription. A biosynthetic operon such as trp can instead be repressed when an end product is abundant. These examples distinguish regulatory logic from a claim that every bacterial gene has the same switch.
Specific promoter regulation implements broader expression control.
Transcription begins through regulated recognition of promoter DNA and recruitment of RNA polymerase. Bacterial sigma factors help promoter recognition; eukaryotic nuclear transcription uses specialized polymerases and transcription factors. RNA is synthesized 5′→3′ from one DNA template strand, with initiation, elongation and termination as distinct stages.
Promoter recruitment connects to transcriptional regulation.