Molecular analysis and organization of the sigmaB operon in Staphylococcus aureus.
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.
Senn
Maria Magdalena
MM
Department of Medical Microbiology, University of Zürich, Switzerland.
Giachino
Philipp
P
Homerova
Dagmar
D
Steinhuber
Andrea
A
Strassner
Jochen
J
Kormanec
Jan
J
Flückiger
Ursula
U
Berger-Bächi
Brigitte
B
Bischoff
Markus
M
D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D015152:Blotting, Northern; D015153:Blotting, Western; D015964:Gene Expression Regulation, Bacterial; D006168:Guinea Pigs; D006358:Hot Temperature; D009876:Operon; D010744:Phosphoric Monoester Hydrolases / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic; D012329:RNA, Bacterial / Q000032:analysis; D012333:RNA, Messenger / Q000032:analysis; D012492:Salts; D012808:Sigma Factor / Q000235:genetics* / Q000378:metabolism; D013203:Staphylococcal Infections / Q000382:microbiology; D013211:Staphylococcus aureus / Q000235:genetics* / Q000502:physiology
D001426:Bacterial Proteins; D012329:RNA, Bacterial; D012333:RNA, Messenger; D012492:Salts; D012808:Sigma Factor; D010744:Phosphoric Monoester Hydrolases; C022394:phosphoserine phosphatase