JAC Advance Access originally published online on February 25, 2003
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Journal of Antimicrobial Chemotherapy (2003) 51, 791-802
© 2003 The British Society for Antimicrobial Chemotherapy
Analyses of ampC gene expression in Serratia marcescens reveal new regulatory properties
Center for Research in Anti-Infectives & Biotechnology, Department of Medical Microbiology and Immunology, Creighton University School of Medicine, Omaha, NE 68178, USA
Received 18 June 2002; returned 10 August 2002; revised 19 December 2002; accepted 24 December 2002
Serratia marcescens encodes an inducible, chromosomal ß-lactamase, ampC. Studies addressing the regulation of inducible ampC genes have focused primarily on Enterobacter cloacae and Citrobacter freundii. The purpose of this study was to clone and sequence the ampC, ampR and intergenic region of S. marcescens and examine both inducible and basal level ampC expression. Sequence analysis of the S. marcescens ampC gene identified an extended 5' untranslated region (UTR) of 126 nucleotides, which formed a prominent stemloop structure. Induction of ampC expression required AmpR, and the start of transcription was determined using primer extension analysis. In vivo half-life analysis revealed that the half-life of the S. marcescens ampC transcript was 7 min. Confirmation of the in vivo half-life and the role of the stemloop structure in the 5' UTR was demonstrated by comparing transcript half-life and luciferase expression between a wild-type (WT) and a 5' UTR stemloop deletion mutant. These data demonstrated that the stemloop structure was involved in transcript stability. Taken together, these findings indicate that constitutive expression of S. marcescens ampC is regulated by both transcriptional initiation and post-transcriptional events.
Keywords: ampC, ß-lactamase, Gram-negative bacteria, regulation
* Corresponding author. Tel: +1-402-280-5837; Fax: +1-402-280-1875; E-mail:ndhanson@creighton.edu
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