Attenuator (genetics)

In genetics, attenuation is a regulatory mechanism for some bacterial operons that results in premature termination of transcription.

Ribosome-mediated attenuation of the trp operon relies on the fact that, in bacteria, transcription and translation proceed simultaneously.

Depending on the metabolic conditions, the attenuator either stops transcription at that point or allows read-through to the structural gene part of the mRNA and synthesis of the appropriate protein.

Attenuation is a regulatory feature found throughout Archaea and Bacteria causing premature termination of transcription.

[2] Attenuators are 5'-cis acting regulatory regions which fold into one of two alternative RNA structures which determine the success of transcription.

There are now many equivalent examples where the translation, not transcription, is terminated by sequestering the Shine-Dalgarno sequence (ribosomal binding site) in a hairpin-loop structure.

Most of these attenuators are inhibitory and are employed by genes for biosynthetic enzymes or transporters[3] whose expression is inversely related to the concentration of their corresponding metabolites.

These elements are bound by specific uncharged tRNAs and modulate the expression of corresponding aminoacyl-tRNA synthetase operons.

[2] .. karima eric discovery Temperature dependent loop formations introduce temperature-dependence in the expression of downstream operons.

All such elements act in a translation-dependent manner by controlling the accessibility of the Shine-Dalgarno sequence, for example the expression of pathogenicity islands of some bacteria upon entry to a host.

[3][7] Recent data predict the existence of temperature-dependent alternative secondary structures (including Rho-independent terminators) upstream of cold shock proteins in E.

Attenuation is made possible by the fact that in prokaryotes (which have no nucleus), the ribosomes begin translating the mRNA while RNA polymerase is still transcribing the DNA sequence.

At the beginning of the transcribed genes of the trp operon is a sequence of 140 nucleotides termed the leader transcript (trpL).

If the ribosome attempts to translate this peptide while tryptophan levels in the cell are low, it will stall at either of the two trp codons.

To ensure that the ribosome binds and begins translation of the leader transcript immediately following its synthesis, a pause site exists in the trpL sequence.

[10] Research conducted on microRNA processing provides evidence of eukaryotic attenuation; after co-transcriptional endonucleolitical cleavage by Drosha 5'->3' exonuclease XRN2 may terminate further transcription by torpedo mechanism.