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R-factor mutant capable of specifying hypersynthesis of penicillinase
Abstract:
The physical characteristics of a mutant, R(M201-2), capable of conferring high and stable ampicillion resistance was analyzed. The R(M201-2) and its parent R-factor deoxyribonucleic acid (DNA) could be isolated as an extrachromosomal and covalently closed circular form. Their buoyant densities were both 1.712 g/cm(3), and their molecular weights were about 82 x 10(6) and 64 x 10(6), respectively, when measured by CsCl and sucrose density gradient analyses. The contour lengths by electron microscopy were 35.9 +/- 0.6 and 31.0 +/- 0.6 mum, respectively. By using the extracted R-factor DNA, the mutant and parent characters were transformable to another Escherichia coli strain. The mutant R factor showed an increased amount of DNA even after conjugal transfer to Proteus. An increase in the size of R-factor DNA was thus considered to be the cause of the high level of ampicillin resistance.
Insights
A mutant R-factor DNA (deoxyribonucleic acid) exhibits increased size, correlating with high ampicillin resistance. This enhanced R-factor DNA is stable and transferable, impacting bacterial resistance mechanisms.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- R-factors are plasmids conferring antibiotic resistance.
- Ampicillin resistance is a significant challenge in bacterial infections.
- Understanding R-factor characteristics is crucial for combating antibiotic resistance.
Purpose of the Study:
- To analyze the physical characteristics of a mutant R-factor (R(M201-2)) conferring high ampicillin resistance.
- To determine the relationship between R-factor DNA properties and ampicillin resistance levels.
Main Methods:
- Isolation of R-factor deoxyribonucleic acid (DNA) in covalently closed circular form.
- Buoyant density measurement using Cesium Chloride (CsCl) density gradient.
- Molecular weight determination via sucrose density gradient analysis.
- Electron microscopy for contour length measurement.
- Transformation experiments to assess character transferability.
Main Results:
- The mutant R(M201-2) and parent R-factor DNA were isolated as extrachromosomal, covalently closed circles.
- Both R-factors showed a buoyant density of 1.712 g/cm³.
- Molecular weights were approximately 82 x 10⁶ (mutant) and 64 x 10⁶ (parent).
- Contour lengths measured 35.9 ± 0.6 µm (mutant) and 31.0 ± 0.6 µm (parent).
- Mutant and parent R-factor DNA characters were transformable to Escherichia coli.
- The mutant R-factor demonstrated increased DNA content post-conjugal transfer.
Conclusions:
- The increased size of the mutant R-factor DNA is associated with high-level ampicillin resistance.
- R-factor DNA size is a key factor in conferring stable and high antibiotic resistance.
- Characterization of R-factors aids in understanding and potentially overcoming antibiotic resistance mechanisms.