| Summary: | Pseudomonas acidovorans was shown to be deficient in a number of enzymes of the salvage pathways of nucleic acid metabolism. These included uridine phosphorylase, purine nucleoside phosphorylase, cytidine (deoxycytidine) deaminase, and thymidine phosphorylase. The absence of uridine kinase and deoxycytidine kinase was also indicated.
Pyrimidine requiring mutants were isolated and pyrimidine substitution
patterns were examined in these auxotrophs. Concentrations of uracil of 50 µg/ml and greater had the unusual effect of inhibiting the growth of these strains, whereas no effect occurred with the wild-type. An inhibitory effect on the wild-type did result, however, when deoxyadenosine or adenosine was added at critical concentrations.
Obligate thymidine auxotrophs were isolated using an adaptation of the aminopterin technique. These strains required very high concentrations
of thymidine (250 to 1000 µg/ml) for growth.
No change in the amount of aspartate transcarbamylase activity occurred during growth in the presence or absence of added uracil. No inhibition of aspartate transcarbamylase activity was evident in the presence of various nucleotides.
Infection of cells by bacteriophage 0W-14 resulted in the apparent synthesis of a phage encoded thymidylate synthetase. In addition, an activity corresponding to deoxyuridyl ate hydroxymethylase was indicated. Thymidine was not a precursor for 5(4-aminobutylaminomethyl) uracil but the base was efficiently labelled by radioactive uracil or deoxyuridine.
Pool studies indicated that the biosynthesis of the base occurred at the nucleotide level rather than the macromolecular level. === Science, Faculty of === Microbiology and Immunology, Department of === Graduate
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