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We isolated promoters inducible by paraquat, a superoxide radical generating agent, from Escherichia colt [Koh, Y. S., and Roe, J. H. (1993) Korean J. MicrobioL 31, 267-273]. These promoter clones were named pgi5, pgil5, and pgi34 where pqi denotes paraquat-inducible genes. Mapping analysis using the E. colt phage library made by Kohara revealed that they are located at about 21, 53, and 18 min on the chromosome, respectively. pgi5 gene was cloned from the Kohara phage E2E5. We constructed an operon fusion of E colt lacZ gene to pgi5 promoter to monitor transcriptional level of the gene in a single copy state. Transcription from pgi5 promoter was induced about 4-fold by 780 M paraquat. Other superoxide generators such as menadione and plumbagin or ethanol also induced the expression of 0-galactosidase in this fusion strain. On the other hand, no significant induction was observed by treatment with hydrogen peroxide and heat shock. Induction of P-galactosidase was significantly reduced by introducing mutations Asox-8::cat or soxS3::Tn10 into the fusion strain, indicating that this gene is a member of the soxRS regulon.
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