Characterization of the Small Untranslated RNA RyhB and Its Regulon inVibrio cholerae

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Abstract
Numerous small untranslated RNAs (sRNAs) have been identified inEscherichia coliin recent years, and their roles are gradually being defined. However, few of these sRNAs appear to be conserved inVibrio cholerae, and both identification and characterization of sRNAs inV. choleraeremain at a preliminary stage. We have characterized one of the few sRNAs conserved betweenE. coliandV. cholerae: RyhB. Sequence conservation is limited to the central region of the gene, and RyhB inV. choleraeis significantly larger than inE. coli. As inE. coli,V. choleraeRyhB is regulated by the iron-dependent repressor Fur, and it interacts with the RNA-binding protein Hfq. The regulons controlled by RyhB inV. choleraeandE. coliappear to differ, although some overlap is evident. Analysis of gene expression inV. choleraein the absence of RyhB suggests that the role of this sRNA is not limited to control of iron utilization. Quantitation of RyhB expression in the suckling mouse intestine suggests that iron availability is not limiting in this environment, and RyhB is not required for colonization of this mammalian host byV. cholerae.