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KMID : 0545120030130040598
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Journal of Microbiology and Biotechnology
2003 Volume.13 No. 4 p.598 ~ p.606
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Molecular Analysis of Salmonella Enterotoxin Gene Expression
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LIM, SANGYONG
SEO, HOSEONG/YOON, HYUNJIN/CHOI, SANGHO/HEU, SUNGGI/RYU, SANGRYEOL
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Abstract
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Salmonella encodes an enterotoxin (Stn) which possesses biological activity similar to the cholera toxin. Stn contributes significantly to the overall virulence of S. typhimurium in a murine model. The production of Stn is enhanced in a high-osmolarity medium and by contact with epithelial cells. In the present study, the in vitro and in vivo transcriptional regulations of the stn promoter revealed two promoters, P1 and P2. The P1 promoter identified by a primer extension analysis of stn mRNA exhibited a switching mechanism in vivo. Depending on the growth stage, transcription was initiated from different start sites termed P1_S and P1_E. P1_S, recognized by RNA polymerase containing σ^S(Eσ^S), and P1_E, recognized by Eσ^(70), were activated during the stationary and exponential phases, respectively, while P1_S and P1_E were both negatively regulated by CRP.cAMP and H-NS. Results revealed that P1_s was the responsible promoter activated under a high osmolarity and low pH. The P2 promoter was identified 45 nucleotides downstream from P1_E and negatively controlled by CRP. cAMP in vitro. No P2 activity was detected in vivo. The regulation of stn expression monitored using a Pstn::egfp fusion indicated that Eσ^S was required for the induction of stn and various factors were involved in stn regulation inside animal cells.
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