Little information is available concerning the metabolic fate of radiation-induced thymine base damage products once they have been excised from DNA. The present study was an attempt to determine whether or not thymine-requiring mutants of Escherichia coli could grow on dihydrothymine (DHT) and thymine glycol (TG) by "salvaging" the altered thymines. A second test of thymine product utilization was prevention of thymineless radiosensitization. Results showed that very low growth of Thy cells on DHT or TG could be explained by the presence of ≤1% contaminating thymine in the mixtures. Radiation dose-modification factors (DMFs) for thyA cells fed DHT or TG for 3 h were 1.38 ± 0.28 and 1.26 ± 0.24, respectively, whereas the DMF for 3 h thymine-starved cells was 1.63 ± 0.05. The small (~25%) amelioration of thymineless radiosensitization observed in DHT- or TG-fed cells could probably be explained by contaminating thymine in the medium. Although DHT is a normal metabolite in some cells, neither DHT nor TG could be used efficiently by thymine-requiring cells in the protocol presented.

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