Attenuator
Definition and meaning of Attenuator in chemistry.
An attenuator is a regulatory DNA sequence in prokaryotes that controls transcription by forming alternative secondary structures in RNA that either terminate or allow transcription to proceed.
In more detail
Attenuation is a transcriptional control mechanism that senses nutrient availability through coupled transcription-translation; the most famous example is the trp (tryptophan) operon in E. coli, where the leader region contains codons for rare amino acids. When the amino acid is abundant, ribosomes quickly translate the leader, causing the mRNA to fold into a terminator hairpin that stops transcription; when the amino acid is scarce, ribosomes stall, allowing an antiterminator structure to form instead, permitting full transcription. Similar attenuation mechanisms regulate other amino acid biosynthesis operons (his, leu, phe).
Key facts
| Field | Biochemistry |
|---|---|
| Primary mechanism | Transcriptional attenuation via RNA secondary structure |
| Key model system | E. coli trp operon |
In the E. coli trp operon, high tryptophan levels cause rapid ribosome translation of the leader region, triggering formation of a terminator stem-loop that halts RNA polymerase, preventing transcription of the downstream tryptophan biosynthetic enzymes.
Frequently asked questions
How does the attenuator detect amino acid levels?
The attenuator senses amino acid availability indirectly through ribosome stalling on rare codons, stalling during transcription changes the mRNA secondary structure to an antiterminator configuration.
Are attenuation mechanisms found beyond the trp operon?
Yes, similar attenuation mechanisms regulate other amino acid biosynthesis operons in bacteria (his, leu, phe operons), though the specific details vary.