Discuss riboswitches.

ANSWER: Riboswitches are a naturally occurring class of aptamers. Aptamers are synthetic oligonucleotides, usually RNA, which fold into very specific three-dimensional structures that selectively bind ligands with high affinity. Riboswitches are conserved regions of mRNAs that reversibly bind specific metabolites and coenzymes and usually act as regulators of gene expression. Riboswitches are usually buried within the 5'- or 3'-untranslated regions of the mRNAs whose expression they regulate. Binding of the metabolite to the riboswitch typically blocks expression of the mRNA.

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