| Popis: |
Ribo-regulators are defined as any RNA molecule that is capable of controlling the expression of a target gene(s) and/or the activity of a target protein. Ribo-regulators are found in every domain of life and, in bacteria, have been shown to have a role in many important processes including virulence, metabolism, iron-acquisition and stress responses. Ribo-regulators can be divided into two major groups, cis-encoded riboregulators and trans-encoded ribo-regulators. trans-encoded ribo-regulators are generally referred to as small RNAs (sRNAs) and consist of RNA molecules that bind target transcripts via complimentary base-pairing and those that sequester specific proteins. Shigella species are the etiological agents of shigellosis, severe bacillary dysentery that affects 165 million people worldwide each year and causes 1.1 million deaths. Infection by Shigella species requires the coordinated production of virulence factors, a process controlled largely by the VirF/VirB regulatory cascade. VirF promotes the transcription of virB, a gene encoding the transcriptional de-repressor of many Shigella virulence genes including those encoding the Type Three Secretion System. S. dysenteriae is known to produce several sRNAs that affect the expression of virulence genes including RyhB, a sRNA known to modulate the expression of virB. In Chapter 2 of this work the mechanism by which RyhB-dependent regulation of virB expression occurs is demonstrated to be independent of VirF activity. Additionally, it is shown that nucleic acid sequences within the virB open reading frame are necessary for RyhB-dependent regulation. In Chapter 3 of this work the first twin sRNAs unique to S. dysenteriae, RyfA1 and RyfA2, are characterized. RyfA1 and RyfA2 are nearly identical in sequence and are produced predominately during logarithmic growth. RyfA1 and RyfA2 are shown to have unique and reciprocal effects on the growth of S. dysenteriae. The twin sRNAs affect virulence in unique ways as measured in tissue cultures assays. Finally, it is demonstrated that each RyfA molecule inhibits production of the other. Results presented within represent a unique and valuable addition to the understanding of Shigella ribo-regulation and virulence. |
