Transcription of the gene mediating methicillin resistance in Staphylococcus aureus (mecA) is corepressed but not coinduced by cognate mecA and beta-lactamase regulators

Resistance to beta-lactam antibiotics in staphylococci is mediated by mecA and blaZ, genes encoding a penicillin-binding protein (PBP2a) with low beta-lactam affinity and beta-lactamase, respectively. The mec and bla regulators, mecR1-mecI and blaR1-blaI, respectively, encode inducer-repressors with...

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Bibliographic Details
Published in:Journal of bacteriology 2001-12, Vol.183 (23), p.6862-6868
Main Authors: McKinney, T K, Sharma, V K, Craig, W A, Archer, G L
Format: Article
Language:English
Subjects:
Bacteria
Bacterial Proteins
Bacteriology
beta-Lactamases - genetics
BlaR1-BlaI protein
blaZ gene
Carrier Proteins - genetics
Drug resistance
Gene Expression Regulation, Bacterial
Genes
Genetics and Molecular Biology
Hexosyltransferases
Lac Operon
mecA gene
MecR1-MecI protein
methicillin
Methicillin Resistance - genetics
Microbiology
Muramoylpentapeptide Carboxypeptidase - genetics
Penicillin-Binding Proteins
Peptidyl Transferases
Promoter Regions, Genetic
Staphylococcus aureus
Transcription, Genetic
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Summary:Resistance to beta-lactam antibiotics in staphylococci is mediated by mecA and blaZ, genes encoding a penicillin-binding protein (PBP2a) with low beta-lactam affinity and beta-lactamase, respectively. The mec and bla regulators, mecR1-mecI and blaR1-blaI, respectively, encode inducer-repressors with sufficient amino acid homology to suggest that they could coregulate PBP2a production. In order to test this hypothesis, plasmids containing mec and bla regulatory sequences were introduced into Staphylococcus aureus containing a chromosomal mecA-lacZ transcriptional fusion. Corepression was confirmed by demonstrating a gene dosage-dependent reduction in beta-galactosidase activity by either MecI or BlaI and additive repression when both were present. Both MecI-MecI and BlaI-BlaI homodimer and MecI-BlaI heterodimer interactions were demonstrated in the yeast two-hybrid assay, and purified MecI and BlaI protected the same mec promoter-operator sequences. However, MecI was approximately threefold more effective at mecA-lacZ transcriptional repression than was BlaI. While MecI and BlaI displayed similar activity as repressors of mecA transcription, there was a marked difference between MecR1 and BlaR1 in the rate and specificity of induction. Induction through BlaR1 by a beta-lactam was 10-fold greater than through MecR1 at 60 min and was 81% of maximal by 2 h, while induction through MecR1 never exceeded 20% of maximal. Furthermore, complementation studies showed that MecI- or BlaI-mediated mecA transcriptional repression could be relieved by induction through homologous but not heterologous sensor-inducer proteins, demonstrating the repressor specificity of induction.
ISSN:0021-9193
1098-5530
DOI:10.1128/JB.183.23.6862-6868.2001