Abstract
Although riboswitches have long been known to regulate translation initiation and transcription termination, a growing body of evidence indicates that they can also control bacterial RNA lifetimes by acting directly to hasten or impede RNA degradation. Ligand binding to the aptamer domain of a riboswitch can accelerate RNA decay by triggering a conformational change that exposes sites to endonucleolytic cleavage or by catalyzing the self-cleavage of a prefolded ribozyme. Alternatively, the conformational change induced by ligand binding can protect RNA from degradation by blocking access to an RNA terminus or internal region that would otherwise be susceptible to attack by an exonuclease or endonuclease. Such changes in RNA longevity often accompany a parallel effect of the same riboswitch on translation or transcription. Consequently, a single riboswitch aptamer may govern the function of multiple effector elements (expression platforms) that are co-resident within a transcript and act independently of one another.