The two-component quorum sensing (QS) system, first described in the marine bacterium Vibrio harveyi and evolutionarily conserved among members of the genus Vibrio, has been best studied in the human pathogen Vibrio cholerae (1, 2). In the V. cholerae QS system, the response to the accumulation of extracellular autoinducers triggers a signaling cascade resulting in the transcription of four small regulatory RNAs (sRNAs). Our results support the model that the QS sRNAs bind to the 5' untranslated region of multiple mRNAs and alter the fate of one in a positive manner and several others in a negative manner. This mechanism ensures the proper timing of the QS response, which includes the expression of traits critical for virulence and for the formation of biofilms (2-6).