Transcription Termination and Attenuation

Transcription termination is the step in which RNA polymerase stops synthesis and releases the completed RNA and the template, defining where a transcript ends. Attenuation is a related regulatory strategy, prominent in bacteria, in which premature termination within a leader region adjusts how much of a downstream gene is transcribed in response to cellular conditions.

Definition

Transcription termination, genetic is the process by which RNA polymerase ceases RNA synthesis and dissociates from the DNA template, releasing the transcript; attenuation is the regulation of gene expression through controlled premature termination of transcription before the polymerase reaches the structural genes.

Scope

The topic covers the mechanisms that end transcription, bacterial intrinsic (hairpin-dependent) and Rho-dependent termination, eukaryotic termination coupled to 3'-end cleavage and polyadenylation, and regulatory premature termination including attenuation and antitermination. It treats these mechanisms at a reference-educational level and not as clinical guidance.

Core questions

• What signals tell RNA polymerase to stop and release its transcript?
• How do bacteria use premature termination (attenuation) to regulate gene expression?
• How is eukaryotic termination coupled to processing of the RNA 3' end?

Key concepts

• Intrinsic (hairpin-dependent) termination
• Rho-dependent termination
• Attenuation and leader peptides
• Antitermination
• Riboswitches
• 3'-end cleavage and polyadenylation
• Polymerase pausing

Mechanisms

In bacteria, intrinsic terminators form a GC-rich RNA hairpin followed by a uracil-rich tract that destabilises the elongation complex, while Rho-dependent termination uses the Rho helicase to translocate along the transcript and dislodge polymerase; antitermination factors can override these signals. Attenuation regulates expression by letting alternative RNA secondary structures in a leader region either favour or prevent terminator formation, often coupled to translation of a short leader peptide or to small-molecule sensing by a riboswitch. In eukaryotes, termination of protein-coding genes is coupled to recognition of the polyadenylation signal and cleavage of the nascent RNA, after which the polymerase is released; in all systems, polymerase pausing is closely tied to the control of where and whether termination occurs.

Clinical relevance

Termination and attenuation mechanisms are studied as targets for antimicrobials and as sources of regulatory variation; defective 3'-end formation and aberrant termination can perturb gene expression in disease. This entry is a reference description of mechanisms and is not a basis for treatment decisions.

History

Attenuation was defined through studies of bacterial amino-acid biosynthetic operons, building on the regulatory logic of the 1961 operon model, while the mechanisms of intrinsic and Rho-dependent termination were established by bacterial transcription biochemistry. In eukaryotes, work on 3'-end processing linked termination to polyadenylation, and modern reviews synthesise termination, antitermination and elongation control.

Key figures

• Charles Yanofsky
• Nick J. Proudfoot
• Irina Artsimovitch
• John T. Lis

Seminal works

• santangelo-artsimovitch-2011
• proudfoot-2011

Frequently asked questions

What is the difference between intrinsic and Rho-dependent termination?

Intrinsic termination relies on an RNA hairpin and a uracil-rich tract that destabilise polymerase on their own, while Rho-dependent termination requires the Rho protein to pull polymerase off the template.

How does attenuation regulate a gene?

Attenuation lets the cell choose, via alternative RNA structures in a leader region, whether transcription terminates early or continues into the structural genes, tuning expression to conditions such as amino-acid availability.