Regulatory RNAs in bacteria represent a diverse group of molecules that act through a variety of intricate mechanisms to modulate a broad range of physiological responses. Some regulatory RNAs act to modulate protein function, often by acting as molecular mimics of other nucleic acids that are regulatory targets of the protein and thus capturing the protein in an unproductive complex (Babitzke & Romeo, 2007). The majority of regulatory RNAs characterized to date act by basepairing with target messenger RNAs (mRNAs) to modulate their stability and/or translation (Papenfort & Vogel, 2010, Waters & Storz, 2009). Base-pairing regulatory RNAs can be divided into cis- and trans-acting RNAs. Well characterized groups of cis-acting regulatory RNAs include riboswitches, which are regulatory elements encoded within an mRNA that can control translation by adopting alternative structures in response to signals such as temperature or the presence of small molecules specifically bound by the riboswitch (Grundy & Henkin, 2006). Other cis-acting RNAs include antisense encoded RNAs, which are transcribed from the opposite strand within or near the target coding sequence and therefore contain perfect sequence complementarity to the target mRNA (Thomason & Storz, 2010).