m Both attenuation and riboswitches rely on changes in the secondary structure o
ID: 34874 • Letter: M
Question
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Both attenuation and riboswitches rely on changes in the secondary structure of the leader regions of mRNA to regulate gene expression.
Part A
Compare and contrast the specific mechanisms in these two types of regulation.
Drag the appropriate items to their respective bins.
bins are attenuation, riboswitch, or both
the items are , is sensitive to intercellular concentrations of tRNAtrp,
5'-region of a forming mRNA can interact with a ligand
involves the formation of exclusive stem-loop structure at the 5'-portion of tryptophan mRNA
can recognize a large range of ligands such as amino acids, purines, viatmin cofactors, and metal ions
Explanation / Answer
is sensitive to intercellular concentrations of tRNAtrp,- attenuation
5'-region of a forming mRNA can interact with a ligand - riboswitches
involves the formation of exclusive stem-loop structure at the 5'-portion of tryptophan mRNA-attenuation
can recognize a large range of ligands such as amino acids, purines, viatmin cofactors, and metal ions - riboswitches
Attenuation (in genetics) is a proposed mechanism of control in some bacterial operons which results in premature termination of transcription and which is based on the fact that, in bacteria, transcription and translation proceed simultaneously.
Attenuation involves a provisional stop signal (attenuator), located in the DNA segment that corresponds to the leader sequence of mRNA. During attenuation, the ribosome becomes stalled (delayed) or halts in the attenuator region in the mRNA leader. Depending on the metabolic conditions, the attenuator either stops transcription at that point or allows a read-through to the structural gene part of the mRNA and synthesis of the appropriate protein of imterest.
Attenuation is a regulatory mechanism or feature found throughout the groups Archaea and Bacteria causing premature termination of transcription. Attenuators are 5'-cis acting regulatory regions which fold into one of two alternative RNA structures which determine the success of transcription.The folding is modulated by a sensing mechanism producing either a Rho-independent terminator, resulting in interrupted transcription and a non-functional RNA product; or an anti-terminator structure, resulting in a functional RNA transcript.
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. While not meeting the previous definition of (transcriptional) attenuation, these are now considered to be variants of the same phenomena. Attenuation is an ancient regulatory system, prevalent in many bacterial species providing fast and sensitive regulation of gene operons and is commonly used to repress genes in the presence of their own product (or a downstream metabolite).
Riboswitches- These regulatory elements in the modern world are most commonly found in the 5?-untranslated regions of bacterial mRNAs, directly interacting with metabolites as a means of regulating expression of the coding region via a secondary structural switch.Life in an RNA world would have relied on RNA as both a medium for heritable genetic information and chemical catalysis. In addition to these functions, life would have had to react to changing environmental conditionsthat is, be capable of regulating biological functions.
Insights into how RNA can accomplish this crucial task have been revealed through recent discoveries that this molecule accomplishes a wide variety of regulatory functions in modern biology. One of the most striking recent examples of how RNA regulates gene expression was revealed by the discovery of riboswitches, a common means of genetic regulation at the mRNA level in the bacterial kingdom.
Riboswitches are elements commonly found in the 5?-untranslated region (UTR) of mRNAs that exert their regulatory control over the transcript in a cis-fashion by directly binding a small molecule ligand.
The typical riboswitch contains two distinct functional domains. The effector molecule is recognized by an aptamer domain, which adopts a compact three-dimensional fold to scaffold the ligand binding pocket. As with proteins, these RNA receptors must discriminate between chemically related metabolites with high selectivity to elicit the appropriate regulatory response. A second domain, the expression platform, contains a secondary structural switch that interfaces with the transcriptional or translational machinery. Regulation is achieved by virtue of a region of overlap between these two domains, known as the switching sequence, whose pairing directs folding of the RNA into one of two mutually exclusive structures in the expression platform that represent the on and off states of the mRNA.
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