Characterizing the Effect of theStaphylococcus aureusVirulence Factor Regulator, SarA, on Log-Phase mRNA Half-Lives

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Abstract
Bacterial pathogens regulate virulence factor expression at both the level of transcription initiation and mRNA processing/turnover. WithinStaphylococcus aureus, virulence factor transcript synthesis is regulated by a number of two-component regulatory systems, the DNA binding protein SarA, and the SarA family of homologues. However, little is known about the factors that modulate mRNA stability or influence transcript degradation within the organism. As our entree to characterizing these processes,S. aureusGeneChips were used to simultaneously determine the mRNA half-lives of all transcripts produced during log-phase growth. It was found that the majority of log-phase transcripts (90%) have a short half-life (cis- and/ortrans-acting factors influenceS. aureusmRNA stability. In support of this, it was found that two virulence factor transcripts,cnaandspa, were stabilized in asarA-dependent manner. These results were validated by complementation and real-time PCR and suggest that SarA may regulate target gene expression in a previously unrecognized manner by posttranscriptionally modulating mRNA turnover. Additionally, it was found thatS. aureusproduces a set of stable RNA molecules with no predicted open reading frame. Based on the importance of theS. aureus agrRNA molecule, RNAIII, and small stable RNA molecules within other pathogens, it is possible that these RNA molecules influence biological processes within the organism.

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