| Summary: | <p>Abstract</p> <p>Background</p> <p>Regulation of bacterial gene expression by small RNAs (sRNAs) have proved to be important for many biological processes. <it>Francisella tularensis </it>is a highly pathogenic Gram-negative bacterium that causes the disease tularaemia in humans and animals. Relatively little is known about the regulatory networks existing in this organism that allows it to survive in a wide array of environments and no sRNA regulators have been identified so far.</p> <p>Results</p> <p>We have used a combination of experimental assays and <it>in silico </it>prediction to identify sRNAs in <it>F. tularensis </it>strain LVS. Using a cDNA cloning and sequencing approach we have shown that <it>F. tularensis </it>expresses homologues of several sRNAs that are well-conserved among diverse bacteria. We have also discovered two abundant putative sRNAs that share no sequence similarity or conserved genomic context with any previously annotated regulatory transcripts. Deletion of either of these two loci led to significant changes in the expression of several mRNAs that likely include the cognate target(s) of these sRNAs. Deletion of these sRNAs did not, however, significantly alter <it>F. tularensis </it>growth under various stress conditions <it>in vitro</it>, its replication in murine cells, or its ability to induce disease in a mouse model of <it>F. tularensis </it>infection. We also conducted a genome-wide <it>in silico </it>search for intergenic loci that suggests <it>F. tularensis </it>encodes several other sRNAs in addition to the sRNAs found in our experimental screen.</p> <p>Conclusion</p> <p>Our findings suggest that <it>F. tularensis </it>encodes a significant number of non-coding regulatory RNAs, including members of well conserved families of structural and housekeeping RNAs and other poorly conserved transcripts that may have evolved more recently to help <it>F. tularensis </it>deal with the unique and diverse set of environments with which it must contend.</p>
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