Molecular Analysis and Organization of the {sigma}B Operon in Staphylococcus aureus

• Published in: Journal of bacteriology Vol. 187; no. 23; p. 8006
• Main Authors: Senn, Maria Magdalena, Giachino, Philipp, Homerova, Dagmar, Steinhuber, Andrea
• Format: Journal Article
• Language: English
• Published: Washington American Society for Microbiology 01.12.2005
• Subjects: Bacteriology; Gene expression; Infections; Yeast
• ISSN: 0021-9193; 1098-5530

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 sigBp1, giving rise to a 3.6-kb transcript covering sa2059-sa2058-rsbU-rsbV-rsbW-sigB, and a {sigma}B-dependent promoter, sigBp3, initiating a 1.6-kb transcript covering rsbV-rsbW-sigB. TSP and promoter-reporter gene fusion experiments indicated that a third promoter, tentatively termed sigBp2 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 sigBp1 and sigBp3. In vitro, the sigBp1 promoter was active in the early growth stages, while the sigBp2 and sigBp3 promoters produced transcripts throughout the growth cycle, with sigBp3 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.[PUBLICATION ABSTRACT]