Replication Rapidly Recovers and Continues in the Presence of Hydroxyurea in Escherichia coli

In both prokaryotes and eukaryotes, hydroxyurea is suggested to inhibit DNA replication by inactivating ribonucleotide reductase and depleting deoxyribonucleoside triphosphate pools. In this study, we show that the inhibition of replication in Escherichia coli is transient even at concentrations of 0.1 M hydroxyurea and that replication rapidly recovers and continues in its presence. The recovery of replication does not require the alternative ribonucleotide reductases, NrdEF and NrdDG, or translesion DNA polymerases, Pol II, Pol IV, or Pol V. Ribonucleotides are incorporated at higher frequencies during replication in the presence of hydroxyurea. However, these do not contribute significantly to the observed synthesis or toxicity. Hydroxyurea toxicity was only observed under conditions where the stability of hydroxyurea was compromised and byproducts, known to damage DNA directly, were allowed to accumulate. The results demonstrate that hydroxyurea is not a direct or specific inhibitor of DNA synthesis in vivo, and that the transient inhibition observed is most likely due to a general depletion of iron cofactors from enzymes when 0.1 M hydroxyurea is initially applied. Finally, the results support previous studies suggesting that hydroxyurea toxicity is mediated primarily through direct DNA damage induced by the breakdown products of hydroxyurea, rather than by inhibition of replication or depletion of deoxyribonucleotide levels in the cell