Abstract
The effect of nucleosides, a group of naturally occurring cell constituents, on the frequency of sister-chromatid exchange (SCE) in Chinese hamster ovary (CHO) cells has been studied. Addition of thymidine (TdR) to the culture medium causes a dose-dependent increase and at 100 μM concentration, the SCE frequency is approximately doubled. This effect is totally reversed by 200 μM deoxycytidine (dCdR) suggesting that deoxycytidine starvation is responsible for this enhancing effect. Neither dCdR by itself nor deoxyadenosine (dAdR) or deoxyguanosine (dGdR) up to 300 μM concentrations had any effect on the incidence of SCE. The frequency of SCE induced by 10 −7 M N-methyl- N-nitro-nitrosoguanine (MNNG) is increased 2-fold by the addition of 100 μM TdR and this effect is also cancelled by 200 μM dCdR. These results point to the importance of the balance in DNA-precursor pools for normal DNA synthesis, infidelity of replication and errors in the replication of alkylated DNA increasing when the precursor pools become unbalanced.
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