In the past year, we have made important progress in our understanding of the mechanism of action of two regulatory RNAs that respond to amino acid starvation in a variety of bacteria, including clinically important pathogens of genera such as Bacillus and Vibrio. The glycine riboswitch is thus far unique among gene-regulatory RNAs in that its architecture involves quaternary interactions. We have used solution methods to analyze how these interactions between independently folded, homologous subunits gives rise to function. The T-box riboswitch controls the expression of aminoacyl-tRNA synthetases, the enzymes responsible for specific charging of tRNA with amino acids, in response to intracellular amino acid levels in Gram-positive bacteria. It is essential for cell survival and virulence. Although this mRNA domain was discovered in 1993, it was not until our work published this year that the mechanism by which the T-box specifically recognizes tRNA was elucidated. In addition to resolving a long-standing question mechanistic, our work forms the starting point for analysis of RNA-RNA interactions in biological systems.