Molecular Analysis and Organization of the B Operon in Staphylococcus aureus

Department of Medical Microbiology, University of Zürich, Switzerland.
Journal of Bacteriology (Impact Factor: 2.81). 01/2006; 187(23):8006-19. DOI: 10.1128/JB.187.23.8006-8019.2005
Source: PubMed


The alternative sigma factor sigma(B) of Staphylococcus aureus controls the expression of a variety of genes, including virulence determinants and global regulators. Genetic manipulations and transcriptional start point (TSP) analyses showed that the sigB operon is transcribed from at least two differentially controlled promoters: a putative sigma(A)-dependent promoter, termed sigB(p1), giving rise to a 3.6-kb transcript covering sa2059-sa2058-rsbU-rsbV-rsbW-sigB, and a sigma(B)-dependent promoter, sigB(p3), initiating a 1.6-kb transcript covering rsbV-rsbW-sigB. TSP and promoter-reporter gene fusion experiments indicated that a third promoter, tentatively termed sigB(p2) and proposed to lead to a 2.5-kb transcript, including rsbU-rsbV-rsbW-sigB, might govern the expression of the sigB operon. Environmental stresses, such as heat shock and salt stress, induced a rapid response within minutes from promoters sigB(p1) and sigB(p3). In vitro, the sigB(p1) promoter was active in the early growth stages, while the sigB(p2) and sigB(p3) promoters produced transcripts throughout the growth cycle, with sigB(p3) peaking around the transition state between exponential growth and stationary phase. The amount of sigB transcripts, however, did not reflect the concentration of sigma(B) measured in cell extracts, which remained constant over the entire growth cycle. In a guinea pig cage model of infection, sigB transcripts were as abundant 2 and 8 days postinoculation as values found in vitro, demonstrating that sigB is indeed transcribed during the course of infection. Physical interactions between staphylococcal RsbU-RsbV, RsbV-RsbW, and RsbW-sigma(B) were inferred from a yeast (Saccharomyces cerevisiae) two-hybrid approach, indicating the presence of a partner-switching mechanism in the sigma(B) activation cascade similar to that of Bacillus subtilis. The finding that overexpression of RsbU was sufficient to trigger an immediate and strong activation of sigma(B), however, signals a relevant difference in the regulation of sigma(B) activation between B. subtilis and S. aureus in the cascade upstream of RsbU.

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Available from: Jan Kormanec, Oct 06, 2015
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    • "The S. aureus sigma B operon resembles that of the homologous B. subtilis operon. It contains σB, an anti-σB factor RsbW, an anti-anti-σB factor RsbV, and RsbU, a Mn2+-dependent phosphatase that positively controls σB activity by dephosphorylating RsbV [80], [81]. The sigma B regulon includes genes directly up-regulated by σB and genes indirectly regulated via σB-dependent expression of regulatory factors such as the SarA transcription factor [76], [77]. "
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    • "Under stress conditions, RsbV is dephosphorylated by one or more specific PP2C-type phosphatases, resulting in the sequestration of RsbW and the activation of σB. This part of this regulatory is conserved in Bacilli (van Schaik et al., 2005), Staphylococcus aureus (Palma and Cheung, 2001; Senn et al., 2005; Pané-Farré et al., 2006) and L. monocytogenes (Wiedmann et al., 1998; Ferreira et al., 2004). However, there are considerable differences in the upstream part of the σB activation pathway (Ferreira et al., 2004; van Schaik et al., 2004a), reflecting differences in the mechanisms of stress sensing and signaling in the various bacteria. "
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    • "TA systems can respond to external stimuli and can be embedded into larger transcriptional networks Besides autoregulatory functions mostly operative in type II representatives, a number of TA systems are also controlled by pleiotropic or specific regulators and/or environmental cues. For example, in S. aureus, the activities of the alternative sigma factor r B and the mazEF system are tightly intertwined (Senn et al., 2005; Donegan & "
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