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Salmonella typhimurium mutants defective in cytidine monophosphate kinase (cmk)
Abstract:
Mutants of Salmonella typhimurium defective in cytidine 5'-monophosphate (CMP) kinase (cmk) have been isolated. The mutants also lack the ability to phosphorylate 2'-deoxyCMP, indicating that one enzyme is responsible for the phosphorylation of both CMP and deoxyCMP to the corresponding diphosphates. In glucose minimal medium the mutants grow at the same rate as the parental strain; however, they excrete large quantities of pyrimidines into the growth medium. Cytidine but not deoxycytidine has been identified among the excreted products. The mutant phenotype suggests that the physiological role of CMP kinase is that of rephosphorylating CMP arising from the breakdown of messenger ribonucleic acid. This proposed role of CMP kinase is supported by the fact that a cmk(-) mutant is much more sensitive to any partial impairment of cytidine 5'-triphosphate synthetase than is the cmk(+) parent strain. The gene cmk has been located on the Salmonella chromosome at 38.5 min. No markers which can be cotransduced with cmk by phage P22 have been found.
Insights
Salmonella mutants lacking cytidine 5'-monophosphate (CMP) kinase excreted excess pyrimidines. This suggests CMP kinase
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- Cytidine 5 -monophosphate (CMP) kinase (cmk) is an enzyme involved in nucleotide metabolism.
- Understanding the specific physiological roles of enzymes like CMP kinase is crucial for comprehending cellular pathways.
- Salmonella typhimurium serves as a model organism for studying bacterial genetics and metabolism.
Purpose of the Study:
- To investigate the function of cytidine 5 -monophosphate (CMP) kinase (cmk) in Salmonella typhimurium.
- To characterize mutants defective in CMP kinase activity.
- To determine the physiological role of CMP kinase in pyrimidine metabolism and RNA turnover.
Main Methods:
- Isolation and characterization of Salmonella typhimurium mutants deficient in CMP kinase (cmk).
- Enzyme assays to assess the phosphorylation of CMP and 2 -deoxyCMP.
- Analysis of excreted metabolites in growth media.
- Genetic mapping of the cmk gene using P22 bacteriophage transduction.
Main Results:
- Mutants lacking CMP kinase (cmk) were unable to phosphorylate both CMP and 2 -deoxyCMP, indicating a single enzyme's role.
- These mutants excreted significant amounts of pyrimidines, primarily cytidine, into the growth medium.
- The cmk(-) mutant exhibited increased sensitivity to impaired cytidine 5 -triphosphate synthetase activity compared to the wild-type.
- The cmk gene was mapped to 38.5 min on the Salmonella chromosome without identifiable cotransducing markers.
Conclusions:
- CMP kinase (cmk) plays a key role in rephosphorylating CMP derived from messenger RNA breakdown.
- The enzyme is essential for efficient pyrimidine nucleotide pools, particularly for DNA and RNA synthesis.
- The genetic locus for cmk in Salmonella typhimurium has been identified.