ABSTRACT

Plasticity of RNA as cis-acting regulatory molecules is because of its extreme structural flexibility, ability to undergo conformational changes and its intrinsic role in the gene expression machinery. Riboswitches are the non-coding portions of mRNAs present at the 5` upstream region that can fold to form complex structure and serve as receptors of specific metabolites. Riboswitches were thought to be evolved through normal vertical descent, numerous genome-specific duplications and horizontal transfers. These are composed of two functional domains, viz., aptamer domain, which serves as a molecular sensor; selectively recognizes its corresponding target molecule within the complex sea of other metabolites and expression platform, which transduce metabolite-binding events into gene-control consequences by allosteric modulation of the structure of the 5′-UTRs. Riboswitches can modulate gene expression by controlling the efficiency of translation initiation, the transcription elongation of mRNA and presumably even the stability and splicing of mRNA transcript. Riboswitch mediated regulation in majority is a form of feedback inhibition. In most prokaryotes, they exploit transcription or translation attenuation, while in eukaryotes; control of splicing reactions plays a key role. Since riboswitches control many fundamental genes and metabolic pathways thus, are potential targets for antimicrobial agents. RNA-based gene control systems might provide a simpler and more versatile architecture for expanding gene control capabilities than that provided by protein-based systems.

Keywords: Riboswitches, gene expression, gene-control, fundamental genes and metabolic pathways