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C F Beck

Publications and source records attributed to C F Beck.

61 records · Page 4Linked to original sources
PubMed1977

Thymidine-requiring mutants of Salmonella typhimurium that are defective in deoxyuridine 5'-phosphate synthesis.

In a Salmonella typhimurium strain made diploid for the thy region by introduction of the Escherichia coli episome, F'15, mutants resistant to trimethoprim in the presence of thymidine were selected. One was shown to be defective in deoxyuridine 5'-phosphate (dUMP) synthesis; it requires deoxyuridine or thymidine for growth and is sensitive to trimethoprim in the presence of deoxyuridine. Genetic studies showed that the mutant is mutated in two genes, dcd and dum, located at 70 and 18 min, respectively, on the Salmonella linkage map. The dcd gene cotransduces 95% with udk, the structural gene for uridine kinase. Both mutations are necessary to create a deoxyuridine requirement, providing evidence for the existence of two independent pathways for dUMP synthesis. Pool studies showed that a dum mutation by itself causes a small decrease in the deoxythymidine 5'-triphosphate (dTTP) pool of the cells, whereas a dcd mutation results in a much more marked decrease. The double mutant dcd dum, when incubated in the absence of deoxyuridine, contains barely detectable levels of dTTP. Enzyme analysis revealed that dcd encodes deoxycytidine 5'-triphosphate deaminase. The gene product of the dum gene has not yet been identified; it does not encode either subunit of ribonucleoside diphosphate reductase or deoxyuridine 5'-triphosphate pyrophosphatase. Mutants deleted for the dcd-udk region of the S. typhimurium chromosome were isolated.

Chromosome Mapping↗
PubMed1975

Deoxycytidine triphosphate deaminase of Salmonella typhimurium. Purification and characterization.

Deoxycytidine triphosphate deaminase (EC 3.5.4., dCTP aminohydrolase) of Salmonella typhimurium LT2 has been pruified 500-fold. The reaction requires the presence of Mg-2plus, Mn-2plus, Ca-2lus, or Co-2plus. Kinetics of the reaction with varying Mg-2plus concentrations, keeping the concentration of dCTP constant, suggests that the true substrate of the reaction is MgdCTP. The dependence of the rate of reaction on dCTP concentration in the presnece of 5-fold excess of Mg-2plus is sigmoid, with a Hill coefficient of 1.7. The enzyme is specifically inhibited by dTTP and dUTP. In the presence of increasing dTTP concentrations the sigmoidicity of the substrate saturation curves increases. With 0.2 and 0.4 mM dTTP the Hill coefficients are 2.6 and 3.0, respectively. Despite several attempts no dissociation of the substrate site and the inhibitor site of the enzyme was achieved.

Binding Sites↗
PubMed1974

Salmonella typhimurium mutants defective in cytidine monophosphate kinase (cmk).

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.

Autoradiography↗
PubMed1972

Metabolism of pyrimidines and pyrimidine nucleosides by Salmonella typhimurium.

The pathways by which uracil, cytosine, uridine, cytidine, deoxyuridine, and deoxycytidine are metabolized by Salmonella typhimurium are established. The various 5-fluoropyrimidine analogues are shown to exert their toxic effects only after having been converted to the nucleotide level, and these conversions are shown to be catalyzed by the same enzymes which similarly convert the natural substrates. Methods for isolating mutant strains blocked in various steps of metabolism of pyrimidine bases and nucleosides are described.

Aminohydrolases↗