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Genetic studies of mutants in a high-affinity methionine transport system in Salmonella typhimurium
1Department of Applied Biology, University of Hull, UK.
Abstract:
A total of 30 metP mutations defective in the high-affinity methionine transport system were linked in P1 transduction to the zaf-1351::Tn10 insertion mutation at min 5-6 on the Salmonella typhimurium chromosome map. The relationship of metP to several other markers in this region was studied. Methionine transport was strongly inhibited by arsenate, suggesting that the metP system belongs to the shock-sensitive category and possesses a periplasmic binding protein. However, other experiments provided less clear cut evidence. Transport activity was only slightly reduced by osmotic shock; a methionine binding activity was detected in shock fluids from the wild-type strain, and although this activity was reduced by 50% in 3 frameshift mutants, mutants without any activity were not found. No differences were detected in the shock fluids of the 30 mutants when examined by SDS-polyacrylamide gel electrophoresis.
Insights
This study investigates Salmonella typhimurium methionine transport, identifying 30 mutations in the metP system. Findings suggest metP is shock-sensitive, but evidence for a periplasmic binding protein was inconclusive.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- The high-affinity methionine transport system in Salmonella typhimurium is crucial for nutrient uptake.
- Understanding the genetic basis and characteristics of this transport system is important for microbial physiology.
Purpose of the Study:
- To characterize the metP gene mutations affecting high-affinity methionine transport in Salmonella typhimurium.
- To investigate the relationship of metP to other chromosomal markers.
- To determine if the metP transport system involves a periplasmic binding protein and its sensitivity to osmotic shock.
Main Methods:
- P1 transduction was used to link 30 metP mutations to a zaf-1351::Tn10 insertion.
- Arsenate inhibition assays were performed to assess transport sensitivity.
- Osmotic shock experiments were conducted to evaluate transport activity and identify periplasmic binding proteins.
- SDS-polyacrylamide gel electrophoresis was used to analyze shock fluid proteins.
Main Results:
- 30 metP mutations were successfully mapped and linked to chromosomal markers.
- Methionine transport showed strong inhibition by arsenate, suggesting shock sensitivity.
- Osmotic shock only slightly reduced transport activity.
- Methionine binding activity was detected in wild-type shock fluids and reduced in some mutants, but not eliminated.
- No significant differences were observed in shock fluid proteins from mutants via SDS-PAGE.
Conclusions:
- The metP transport system in Salmonella typhimurium appears to be shock-sensitive.
- Evidence for a periplasmic binding protein in the metP system was inconclusive.
- Further investigation is needed to fully elucidate the mechanism of high-affinity methionine transport.