Nucleic Acids Research Advance Access originally published online on February 11, 2008
Nucleic Acids Research 2008 36(6):1913-1927; doi:10.1093/nar/gkn050
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Nucleic Acids Research, 2008, Vol. 36, No. 6 1913-1927
© 2008 The Author(s)
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
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Small RNAs encoded within genetic islands of Salmonella typhimurium show host-induced expression and role in virulence
Department of Molecular Genetics and Biotechnology, The Hebrew University-Hadassah Medical School, 91120, Jerusalem, Israel
*To whom correspondence should be addressed. Tel: +97226757212; Fax: +97226757308; Email: shoshy{at}cc.huji.ac.il
Received November 1, 2007. Revised December 25, 2007. Accepted January 24, 2008.
The emergence of pathogenic strains of enteric bacteria and their adaptation to unique niches are associated with the acquisition of foreign DNA segments termed ‘genetic islands’. We explored these islands for the occurrence of small RNA (sRNA) encoding genes. Previous systematic screens for enteric bacteria sRNAs were mainly carried out using the laboratory strain Escherichia coli K12, leading to the discovery of 
80 new sRNA genes. These searches were based on conservation within closely related members of enteric bacteria and thus, sRNAs, unique to pathogenic strains were excluded. Here we describe the identification and characterization of 19 novel unique sRNA genes encoded within the ‘genetic islands’ of the virulent strain Salmonella typhimurium. We show that the expression of many of the island-encoded genes is associated with stress conditions and stationary phase. Several of these sRNA genes are induced when Salmonella resides within macrophages. One sRNA, IsrJ, was further examined and found to affect the translocation efficiency of virulence-associated effector proteins into nonphagocytic cells. In addition, we report that unlike the majority of the E. coli sRNAs that are trans regulators, many of the island-encoded sRNAs affect the expression of cis-encoded genes. Our study suggests that the island encoded sRNA genes play an important role within the network that regulates bacterial adaptation to environmental changes and stress conditions and thus controls virulence.
Pressent address: Ruth Hershberg, Department of Biological Sciences, Stanford University, Serra Mall, Stanford, CA 94305, USA
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