Riboswitches | Structure Function of Riboswitches |

ZOOHCC - 501: Molecular Biology (Theory)

Unit 3: Transcription and Regulatory RNAs

Riboswitches

Riboswitches are genetic elements of RNA molecules that can regulate gene expression in response to specific environmental or cellular signals. They consist of structured RNA domains that act as molecular switches, controlling access to ribosome binding sites on mRNAs. This allows regulation of protein synthesis in response to different conditions.

Riboswitches were first discovered in bacteria and play important roles in regulating many cellular processes, including stress responses, nutrient uptake, and virulence. They have also been found in other organisms, including plants and fungi, and may have similar functions. Riboswitches have attracted a lot of interest from scientists due to their promising applications in synthetic biology and biotechnology. They can be designed to respond to specific signals and conditions, enabling precise control of gene expression in a variety of applications, including: B. Production of therapeutic proteins or development of biosensors.

Riboswitches are non-coding mRNA domains that regulate transcription and translation of downstream genes without protein assistance. Riboswitches can directly bind metabolites and form unique stem-loop or hairpin structures depending on the amount of metabolite present. They have her two distinct domains: metabolite-binding aptamers and expression platforms.

Riboswitches are structured mRNA elements involved in gene regulation that respond to the intracellular concentration of specific small molecules. Binding of their cognate ligand is thought to elicit a global conformational change of the riboswitch, in addition to modulating the fine structure of the binding site.

Examples

Riboswitch ligands include glycine, coenzyme B12, thiamine, flavin mononucleotides, S-adenosylmethionine, and guanine.

Riboswitches are specific components of mRNA molecules that regulate gene expression. Riboswitches are parts of mRNA molecules that can bind and attack small target molecules. An mRNA molecule may contain riboswitches that directly regulate its own expression. Riboswitches demonstrate the ability to regulate RNA by responding to the levels of its target molecules. Riboswitches are natural RNA molecules that enable RNA regulation. Thus, the existence of RNA molecules provides evidence for the hypothesis of the RNA world that RNA molecules are the original molecules and that proteins evolved late in evolution.

Expression platforms regulate transcription or translation by forming anti-terminator or terminator structures. Formation of these structures is dependent on the binding of metabolites to the aptamer. At low concentrations, metabolites do not bind to aptamers. This signals the expression platform to form an anti-terminator structure and proceed with transcription or translation. On the other hand, when metabolites are present at high concentrations, they bind to aptamers. In this case, the expression platform forms a terminator structure followed by a series of uracil residues. This dissociates the RNA polymerase from the transcript and DNA strand, terminating transcription. Expression platforms can also inhibit ribosome binding to transcripts by forming a hairpin structure at the ribosome binding site (also known as the Shine-Dalgarno sequence), thereby preventing translation initiation. Another mechanism by which riboswitches regulate transcription is by acting as an RNA enzyme or ribozyme found in the glmS riboswitch ribozyme. These ribozymes cleave the riboswitch mRNA upon metabolite binding and the remaining mRNA is degraded by RNases, inhibiting translation.

Riboswitches were once thought to be unique to bacteria and archaea, but have recently been found in plants and fungi. To date, only thiamine pyrophosphate (TPP)-specific riboswitches have been found in eukaryotes. Unlike bacteria, eukaryotic genes contain introns so that transcription and translation cannot occur simultaneously in the same transcript. Therefore, these riboswitches regulate transcription through alternative splicing. In some plants, a TPP riboswitch is present in her 3′ untranslated intron region of her THIC gene. Low levels of her TPP mask splice sites near the 5' of the 3' untranslated region, resulting in stable mRNA. However, when high levels of TPP are present, TPP binds to riboswitches and exposes the 5' splice junction of the 3' untranslated region. Removal of the intron creates an unstable mRNA that cannot produce protein.

Wartswitches

Wartswitches are found in bacteria, plants, and certain fungi. The various mechanisms by which riboswitches work can be divided into two main parts, including aptamers and expression platforms. Aptamers are characterized by the ability of the riboswitch to bind directly to its target molecule. When the aptamer binds to its target molecule, it changes the conformation of the expression platform, affecting gene expression. Expression platforms that control gene expression can be switched off or activated depending on the specific function of the small molecule. Various mechanisms by which riboswitches work include:

• Ability to act as a ribozyme and self-cleave when sufficient concentrations of metabolites are present
• Ability to fold mRNA in such a way that the ribosome binding site is inaccessible and prevents translation
• Ability to influence splicing of pre-mRNA molecules

The mechanism by which riboswitches regulate RNA expression can be divided into two major processes involving aptamers and expression platforms.

• Aptamers are characterized by the direct binding of small molecules to their targets.
• Expression platforms are characterized by conformational changes that occur in the target upon aptamer binding that result in either inhibition or activation of gene expression.