Research Interests: RNA-mediated regulation of virulence gene expression in Shigella.

We are actively investigating the role of both cis -encoded and trans -encoded regulatory RNA molecules in controlling the expression of virulence-associated genes in Shigella species . This broad interest has given rise to three independent projects, each of which are detailed below:

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Project #1: Investigate the role of RNA thermometers in controlling virulence gene expression in S. dysenteriae. RNA thermometers are cis- encoded regulatory elements that modulate translation efficiency in response to temperature. Our present studies were the first to identify and characterize a functional RNA thermometer in any Shigella species (Kouse et al, 2013). Specifically, we have demonstrated that the expression of shuA, a gene encoding an outer-membrane heme receptor, is subjected to temperature-dependent post-transcriptional regulation and that this regulation is mediated by the activity of a RNA thermometer harbored within the 5’ untranslated region of the gene. We are currently using knowledge gained in this initial study to identify and characterize additional Shigella RNA thermometers, an approach that will reveal the impact of these ribo-regulators on the physiology and virulence of this human pathogen.

Project #2: Characterize the molecular mechanism underlying RyhB-dependent regulation of virB, a master regulatory of Shigella virulence gene expression.

Our initial studies established that the regulatory small RNA RyhB controls the expression virB , a gene encoding a master regulator of Shigella virulence gene expression (Murphy et al., 2007 and Africa et al., 2011). Subsequent analysis has demonstrated that RyhB-dependent regulation of virB expression is mediated at the level of transcription (Broach et al., 2012), yet the precise regulatory mechanism remains unknown. Ongoing studies in the lab aim to elucidate the potentially novel regulatory mechanism by which RyhB controls the translation of virB.

Project #3: Characterization of RyfA1 and RyfA2, novel tandem duplicate sRNA molecules identified in S. dysenteriae. Preliminary studies have identified RyfA1 and RyfA2, two novel duplicated regulatory small RNA molecules that are encoded in tandem on the chromosome of S. dysenteriae. RyfA1 and RyfA2 share 95% identity with each other and approximately 91% identity with the single RyfA molecule encoded in other Shigella species and related strains of pathogenic Escherichia coli. While RyfA1 and RyfA2 are nearly identical to each other their promoter sequences are differ, suggesting that each regulatory molecule may be expressed under unique environmental conditions, an assertion that is supported by preliminary data. Further studies have confirmed that S. dysenteriae produces both RyfA1 and RyfA2 and suggest that one or both of these molecules influence virulence-associated phenotypes in this human pathogen. Current studies in the laboratory are focused on elucidating the impact of RyfA1 and RyfA2 on the physiology and virulence of S. dysenteriae.