A processive riboantiterminator seeks a switch to make biofilms.

Since the discovery of the first signal-sensing RNA structure by Grundy and Henkin in 1993, the list of cis-acting riboregulators has grown dramatically. Riboswitches fold into elaborate structures and respond to binding of small metabolites by altering the folding pattern of the surrounding transcript, thereby altering the gene expression programme. Riboswitches that use short-range mechanisms to control transcription attenuation and translation initiation and mediate mRNA cleavage have been characterized in many Gram-positive bacteria. Their action typically relies on alternative RNA structures that are differentially stabilized by the ligand binding. In this issue of Molecular Microbiology, Irnov and Winkler describe a novel Bacillus subtilis riboregulator called EAR that shares structural complexity with riboswitches but possesses a unique mechanism of action. EAR increases expression of exopolysaccharide genes and biofilm formation, and appears to act as a processive, long-range antiterminator, the first such example outside of Escherichia coli. While it is unclear whether EAR senses a biofilm-inducing signal, the results suggest that its action depends on yet unidentified auxiliary factors. Interestingly, efficient capsule biogenesis in E. coli and Bacteroides fragilis also depends on processive antiterminators but utilizes the protein-based mechanisms instead.