Riboswitches (Lecture 13)

How does FMN alter the riboswitch to stop transcription

In the absence of FMN base pairing between regions at the base of the riboswitch causes it to assume an antitermination conformation. When FMN binds these sequences do not base pair with eachother and instead with another part of the riboswitch creating the termination conformatin that prevents transcription. (SEE DIAGRAM)

what is a riboswitch

a molecule that is located within the mRNA that can regulate genes independently

what is the difference between attenuation and riboswitches

attenuation- the level of trp is sensed by the ribosome which determines its speed and thus the conformational change riboswitches require direct interaction with the ligand for the conformational change to occur

what is the structure of the riboswitch

consists of an aptamer and an expression platform

what is the role of the riboswitch of B.subtilis ribD

controls the synthesis and transport of riboflavin which is the precursor for FMN

How was it proved that FMN alters the conformation of ribD riboswitch

incubation of RNA containing RFM in vitro with RNA polymerase had higher frequencied of transcriptional termination in the presence of FMN

How does ligand binding to the riboswitch affect transcription

ligand binding allows the termination loop to form so transcription stops

How does ligand binding to the riboswitch affect translation

ligand binding results in the shine dalgarno sequence from being hidden. The shine dalgarno sequence attracts ribosomes to nearby AUG to begin translation. However as it is hidden the ribosome cannot bind and translation is prevented

Is the attenuation of the trp operon a riboswitch

no

what is the role of riboswitches

regulate gene expression by alternative mRNA secondary structure

what are the similarities between attenuation and riboswitches

ribosome senses the trp levels and changes the secondary structure of mRNA affecting transcription

what is an example of a riboswitch. Name the aptamer and ligand

the B.subtilis ribD operon. the aptamer is the RFN element and the ligand is FMN

How does a riboswitch regulate gene expression

the binding of ligands to the aptamer regulates riboswitches. When the ligand is absent gene expression is turned on but when it is present it binds to the aptamer and changes the conformation of the riboswitch including the expression platform. This turns gene expression off (MEMORISE DIAGRAM)

what can be an expression platform in the riboswitch

transcriptional terminator ribosome binding site RNA element that affects gene expression

when will the Rib genes of the B.subtilis ribD operon be repessed

when FMN is high as no more needed thus riboflavin not necessarry

when will the Rib genes of the B.subtilis ribD operon be expressed

when FMN is low as riboflavin must be produced to form more FMN