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J Antimicrob Chemother. 2004 Feb;53(2):197-202. Epub 2004 Jan 16.

Role of the 'cre/blr-tag' DNA sequence in regulation of gene expression by the Aeromonas hydrophila beta-lactamase regulator, BlrA.

Author information

1
Bristol Centre for Antimicrobial Research and Evaluation, Department of Pathology and Microbiology, School of Medical Sciences, University of Bristol, University Walk, Bristol BS8 1TD, UK. Matthewb.Avison@bris.ac.uk

Abstract

OBJECTIVES:

To further understand the mechanisms used to regulate expression of the blr regulon of Aeromonas hydrophila T429125, including three unlinked beta-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 beta-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-beta-lactamase genes being co-ordinately regulated with a normally co-resident beta-lactamase gene, and the first direct evidence for a role of the cre/blr-tag sequence in the regulation of transcription by BlrA.

PMID:
14729737
DOI:
10.1093/jac/dkh077
[Indexed for MEDLINE]

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