Modulation of DNA precursor pools, DNA synthesis, and ultraviolet sensitivity of a repair-deficient CHO cell line by deoxycytidine.

The presence of 2 mM deoxycytidine (CdR) in growth medium substantially increased the deoxycytidine triphosphate (dCTP) and deoxythymidine triphosphate (dTTP) pools in a Chinese hamster ovary cell line, CHO-K1, and in a radiation-sensitive mutant, xrs-5, derived from it (Jeggo et al., 1982). We observed significant differences in alkaline-sucrose gradient profiles of pulse-labeled DNA from unirradiated CHO-K1 and xrs-5 cells. For the latter cell line, a sizable fraction of the DNA synthesized during 5 or 10 min of growth subsequent to a 5-min radiolabeling period was found to co-sediment with large-chromosome DNA. This characteristic of xrs-5 was dramatically reduced by the presence of 2 mM CdR in the culture medium, and the UV resistance of the mutant increased to nearly that of the parent cell line under these culture conditions. These results show that the locus conferring UV-radiation sensitivity to xrs-5 affects DNA replication and that replicative activity and UV-radiation sensitivity are jointly modulated by CdR, possibly through its impact on the size of deoxynucleoside triphosphate pools.