Journal Article

Role of the ‘cre/blr-tag’ DNA sequence in regulation of gene expression by the <i>Aeromonas hydrophila</i> β-lactamase regulator, BlrA

Matthew B. Avison, Pannika Niumsup, Kurshid Nurmahomed, Timothy R. Walsh and Peter M. Bennett

in Journal of Antimicrobial Chemotherapy

Published on behalf of British Society for Antimicrobial Chemotherapy

Volume 53, issue 2, pages 197-202
Published in print February 2004 | ISSN: 0305-7453
Published online February 2004 | e-ISSN: 1460-2091 | DOI:
Role of the ‘cre/blr-tag’ DNA sequence in regulation of gene expression by the Aeromonas hydrophila β-lactamase regulator, BlrA

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Objectives: To further understand the mechanisms used to regulate expression of the blr regulon of Aeromonas hydrophila T429125, including three unlinked β-lactamase genes, ampH, cepH and imiH, and to examine the role of the ‘cre/blr-tag’ DNA sequence (TTCAC) in transcriptional control exerted by the two-component system, BlrAB.

Methods: Genes linked to blrAB-ampH were cloned using standard methods; gene expression was measured by RT–PCR or β-lactamase assays; transcription start sites were determined by reversed-transcript analysis; cepH promoter probe reporter constructs including cre/blr-tag deletions were generated by PCR; and BlrA was overexpressed in Escherichia coli using the pBAD plasmid.

Results: The blrD gene, encoding a putative inner membrane protein, was found to be located downstream of blrAB-ampH. RT–PCR analysis showed that blrD is part of the A. hydrophila blr regulon, and transcript start-point determinations revealed that blr-regulon promoters (including that of blrD) are preceded by at least one cre/blr-tag. Targeted deletion of the 16 bp cepH cre/blr-tag dimer blocked BlrA-induced overproduction of cepH in E. coli.

Conclusions: This is the first report of non-β-lactamase genes being co-ordinately regulated with a normally co-resident β-lactamase gene, and the first direct evidence for a role of the cre/blr-tag sequence in the regulation of transcription by BlrA.

Keywords: Keywords: blr regulon, cre regulon, CreBC, BlrD, cre/blr-tag

Journal Article.  3902 words.  Illustrated.

Subjects: Medical Oncology ; Critical Care

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