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On the ability of Salmonella typhimurium cells to form deoxycytidine nucleotides
Abstract:
It is known that cdd- S. typhimurium mutants selected for resistance to 5-fluorodeoxycytidine (FdCyd) possess no deoxycytidine kinase activity. The present study postulates that this method of screening selects double mutants defective in cytidine deaminase and in deoxycytidine kinase. To prove this hypothesis, the cdd mutant of S. typhimurium was constructed by P1-mediated transfer of ccd- gene into a new genetic background, and the activity of deoxycytidine kinase was assayed. Transductants exhibited no deoxycytidine kinase activity, showing that the absence of this enzyme is not limited to a specific cdd- mutant, but includes all strains of S. typhimurium. The toxicity of FdCyd for the bacterial strains possessing deoxycytidine kinase, as well as the role of nucleoside phosphorylase in nucleotide formation by S. typhimurium, is discussed.
Insights
Salmonella typhimurium mutants resistant to 5-fluorodeoxycytidine (FdCyd) lack deoxycytidine kinase. This study confirms that FdCyd resistance in S. typhimurium selects for dual defects in cytidine deaminase and deoxycytidine kinase.
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- Salmonella typhimurium mutants resistant to 5-fluorodeoxycytidine (FdCyd) are known to lack deoxycytidine kinase activity.
- Previous screening methods for FdCyd resistance may inadvertently select for multiple genetic defects.
Purpose of the Study:
- To investigate whether screening for FdCyd resistance in S. typhimurium selects for double mutants defective in both cytidine deaminase and deoxycytidine kinase.
- To confirm the absence of deoxycytidine kinase activity in a broader range of S. typhimurium strains.
Main Methods:
- Construction of a cdd mutant of S. typhimurium through P1-mediated gene transfer.
- Assay of deoxycytidine kinase activity in the constructed transductants.
- Discussion of 5-fluorodeoxycytidine toxicity and the role of nucleoside phosphorylase.
Main Results:
- Transductants derived from the cdd mutant consistently exhibited no detectable deoxycytidine kinase activity.
- The absence of deoxycytidine kinase activity was demonstrated to be a characteristic of S. typhimurium strains selected for FdCyd resistance, not limited to a single mutant.
Conclusions:
- The screening method for 5-fluorodeoxycytidine resistance in S. typhimurium effectively selects for double mutants lacking both cytidine deaminase and deoxycytidine kinase.
- The findings highlight the importance of understanding enzymatic pathways for drug resistance mechanisms in bacteria.