Related Experiment Videos
Nucleotide sequence and expression of the organomercurial-resistance determinants from a Pseudomonas K-62 plasmid
1Faculty of Pharmaceutical Sciences, Setsunan University, Hirakata, Osaka, Japan.
Abstract:
pMRA17 cloned from Pseudomonas K-62 plasmid pMR26 specified the resistance to both organic and inorganic mercurials. DNA sequence of this broad-spectrum resistant mer operon was determined. The 5504-bp sequence includes six open reading frames (ORFs), five of which were identified as merR, merT, merP, merA and merB in order by analysis of deletion mutants and by comparison with the DNA and amino acid (aa) sequences of previously sequenced mer operons. The merB encoding organomercurial lyase showed a less identity than the other mer genes with those from other broad-spectrum resistance operons. The remaining ORF named merE, located between merA and merB, had no significant homology with the published mer genes and seemed to be a new gene which may involve in phenylmercury resistance. Induction experiments and maxicell analyses of the mer-polypeptides revealed that pMRA17 mer operon expressed mercurial-inducible phenotype and the merB and merE as well as the merA were under the control of MerR which could activate not only by mercuric ion but also by organomercurials.
Insights
This study details the DNA sequence of a broad-spectrum mercury resistance operon from Pseudomonas. A newly identified gene, merE, may play a role in phenylmercury resistance, with the operon regulated by MerR.
Area of Science:
- Microbiology
- Molecular Biology
- Environmental Science
Background:
- Mercury resistance is crucial for microbial survival in contaminated environments.
- Broad-spectrum mercury resistance operons confer protection against both organic and inorganic mercury compounds.
- Understanding the genetic basis of mercury resistance is vital for bioremediation strategies.
Purpose of the Study:
- To determine the complete DNA sequence of the mer operon from Pseudomonas K-62 plasmid pMRA17.
- To identify and characterize the genes responsible for broad-spectrum mercury resistance.
- To investigate the regulatory mechanisms controlling the expression of the mercury resistance operon.
Main Methods:
- DNA sequencing of the pMRA17 plasmid.
- Analysis of open reading frames (ORFs) and comparison with known mer operons.
- Deletion mutant analysis and maxicell experiments to determine gene function and polypeptide expression.
- Amino acid sequence comparison to assess gene homology.
Main Results:
- The 5504-bp mer operon contains six ORFs: merR, merT, merP, merA, merE, and merB.
- Five genes (merR, merT, merP, merA, merB) show homology to known mercury resistance genes.
- A novel ORF, merE, located between merA and merB, lacks homology to known mer genes and may be involved in phenylmercury resistance.
- The operon exhibits a mercury-inducible phenotype, with MerR regulating merA, merB, and merE expression in response to mercuric ions and organomercurials.
Conclusions:
- The pMRA17 mer operon provides broad-spectrum resistance to mercury compounds.
- The identification of merE suggests a novel mechanism for phenylmercury resistance.
- The MerR regulator controls the expression of key resistance genes, responding to various mercury species.