Effects of hydroxyurea on DNA synthesis in mouse L-cells

The effect of the anti-metabolite hydroxyurea on DNA synthesis in mouse L-cells has been examined. It was shown previously that when DNA synthesis was diminished to very low levels by treatment with the drug there was preferential incorporation of added [3H]dThd into low molecular weight fragments (Martin, R.F., Radford, I. And Pardee, M. (1977) Biochem. Biophys. Res. Commun. 74, 9-15). On the basis of several criteria it is concluded here that these fragments are a product of semi-conservative nuclear DNA replication. The preferential labelling of DNA fragments, but not their size, is shown to be dependent on the hydroxyurea concentration used. These DNA fragments are also shown, by comparison with normal DNA replication intermediates, to comprise a heterogeneous population of 'larger-than-normal' fragments. Different models to account for these findings are considered and it is concluded that the results are compatible with a loss of coordination of DNA synthesis following drug treatment.