Abstract
Divalent ions fulfill essential cellular roles and are required for virulence by certain bacteria. Free intracellular Mg(2+) can approach 5 mm, but at this level Mn(2+), Ni(2+), or Co(2+) can be growth-inhibitory, and magnesium fluoride is toxic. To maintain ion homeostasis, many bacteria have evolved ion sensors embedded in the 5'-leader sequences of mRNAs encoding ion uptake or efflux channels. Here, we review current insights into these "metalloriboswitches," emphasizing ion-specific binding by structured RNA aptamers and associated conformational changes in downstream signal sequences. This riboswitch-effector interplay produces a layer of gene regulatory feedback that has elicited interest as an antibacterial target.