translational attenuation

Definition

Target type: biologicalprocess

Translational attenuation is a regulatory mechanism analogous to ribosome-mediated transcriptional attenuation. The system requires the presence of a short ORF, called a leader peptide, encoded in the mRNA upstream of the ribosome-binding site and start codon of the gene whose translation is to be regulated. Certain conditions, such as presence of the antibiotic tetracycline in bacteria or amino acid starvation, may cause slowing or stalling of the ribosome translating the leader peptide. The stalled ribosome masks a region of the mRNA and affects which of two alternative mRNA folded structures will form, therefore controlling whether or not a ribosome will bind and initiate translation of the downstream gene. Translational attenuation is analogous to ribosome-mediated transcriptional attenuation, in which mRNA remodeling caused by ribosome stalling regulates transcriptional termination rather than translational initiation. [PMID:15694341, PMID:15805513]

Translational attenuation is a regulatory mechanism that controls gene expression at the level of translation. It involves a decrease in the rate of protein synthesis, often triggered by specific environmental conditions. Here's a detailed explanation:

1. **Mechanism:** Translational attenuation typically relies on the interaction between a ribosome and a specific sequence within the mRNA, known as an attenuator sequence. This sequence contains a series of codons that can be read differently depending on the availability of specific amino acids.
* **Leader Peptide:** Attenuator sequences often precede the coding region for a specific protein and encode a short polypeptide called a "leader peptide." The sequence of the leader peptide plays a crucial role in the attenuation process.
* **Hairpin Structures:** The attenuator region often contains two or more potential hairpin structures (stem-loop structures) that can form within the mRNA. These structures compete for the same region of mRNA.

2. **Regulation:** The formation of these hairpin structures is influenced by:
* **Amino Acid Availability:** When the necessary amino acids are abundant, ribosomes move quickly through the leader peptide sequence, preventing the formation of a specific hairpin structure that would block translation.
* **Limited Amino Acids:** When the necessary amino acids are scarce, the ribosome stalls at specific codons within the leader peptide. This stalling allows time for a different hairpin structure to form, which blocks the ribosome's access to the main coding region.

3. **Examples:**
* **Tryptophan Operon (E. coli):** In bacteria, the tryptophan operon is a classic example of translational attenuation. When tryptophan levels are low, the ribosome stalls at a tryptophan codon within the leader peptide. This allows the formation of a hairpin structure that blocks translation of the tryptophan biosynthesis genes.
* **Other Examples:** Translational attenuation is found in various organisms, including bacteria, archaea, and even eukaryotes. It is often involved in the regulation of amino acid biosynthesis pathways and other metabolic processes.

4. **Significance:** Translational attenuation is an important regulatory mechanism that allows cells to adjust protein synthesis based on the availability of specific nutrients, cofactors, or other essential molecules. It provides a rapid and efficient way to respond to changes in the cellular environment.

By controlling translation initiation, translational attenuation plays a vital role in gene expression and cellular adaptation.'
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